Upgrade sphinx version used in ReadTheDocs.
Upgrade sphinx version used in ReadTheDocs.

According to https://github.com/spatialaudio/nbsphinx/issues/26, this
should fix support for mixing rST and markdown in our docs.

Fixes #668.

mahim97/zulip,brainwane/zulip,vabs22/zulip,reyha/zulip,ryanbackman/zulip,andersk/zulip,vikas-parashar/zulip,AZtheAsian/zulip,sharmaeklavya2/zulip,reyha/zulip,krtkmj/zulip,rht/zulip,niftynei/zulip,niftynei/zulip,christi3k/zulip,brainwane/zulip,j831/zulip,isht3/zulip,zulip/zulip,Vallher/zulip,krtkmj/zulip,Diptanshu8/zulip,cosmicAsymmetry/zulip,dawran6/zulip,samatdav/zulip,shubhamdhama/zulip,SmartPeople/zulip,arpith/zulip,timabbott/zulip,krtkmj/zulip,arpith/zulip,punchagan/zulip,SmartPeople/zulip,andersk/zulip,synicalsyntax/zulip,ahmadassaf/zulip,synicalsyntax/zulip,KingxBanana/zulip,sharmaeklavya2/zulip,AZtheAsian/zulip,eeshangarg/zulip,vaidap/zulip,souravbadami/zulip,jainayush975/zulip,SmartPeople/zulip,ryanbackman/zulip,Diptanshu8/zulip,arpith/zulip,jackrzhang/zulip,vabs22/zulip,Jianchun1/zulip,amanharitsh123/zulip,blaze225/zulip,cosmicAsymmetry/zulip,shubhamdhama/zulip,brockwhittaker/zulip,j831/zulip,Vallher/zulip,showell/zulip,samatdav/zulip,cosmicAsymmetry/zulip,jphilipsen05/zulip,umkay/zulip,timabbott/zulip,paxapy/zulip,brainwane/zulip,krtkmj/zulip,synicalsyntax/zulip,KingxBanana/zulip,samatdav/zulip,vaidap/zulip,sonali0901/zulip,j831/zulip,Galexrt/zulip,hackerkid/zulip,brockwhittaker/zulip,isht3/zulip,Juanvulcano/zulip,blaze225/zulip,dattatreya303/zulip,eeshangarg/zulip,Juanvulcano/zulip,verma-varsha/zulip,dattatreya303/zulip,PhilSk/zulip,TigorC/zulip,brainwane/zulip,calvinleenyc/zulip,ryanbackman/zulip,kou/zulip,peguin40/zulip,showell/zulip,dawran6/zulip,Jianchun1/zulip,Jianchun1/zulip,christi3k/zulip,blaze225/zulip,rishig/zulip,KingxBanana/zulip,amanharitsh123/zulip,reyha/zulip,Vallher/zulip,punchagan/zulip,mohsenSy/zulip,grave-w-grave/zulip,kou/zulip,tommyip/zulip,jrowan/zulip,AZtheAsian/zulip,Diptanshu8/zulip,susansls/zulip,hackerkid/zulip,shubhamdhama/zulip,mahim97/zulip,dhcrzf/zulip,vabs22/zulip,calvinleenyc/zulip,andersk/zulip,Jianchun1/zulip,rht/zulip,amyliu345/zulip,kou/zulip,amanharitsh123/zulip,Galexrt/zulip,vikas-parashar/zulip,niftynei/zulip,dawran6/zulip,Galexrt/zulip,vikas-parashar/zulip,umkay/zulip,amyliu345/zulip,dawran6/zulip,Jianchun1/zulip,zacps/zulip,punchagan/zulip,aakash-cr7/zulip,brockwhittaker/zulip,christi3k/zulip,dattatreya303/zulip,verma-varsha/zulip,Diptanshu8/zulip,rht/zulip,mahim97/zulip,cosmicAsymmetry/zulip,TigorC/zulip,hackerkid/zulip,amyliu345/zulip,mohsenSy/zulip,sup95/zulip,paxapy/zulip,mahim97/zulip,jrowan/zulip,Galexrt/zulip,ahmadassaf/zulip,aakash-cr7/zulip,j831/zulip,jainayush975/zulip,sonali0901/zulip,TigorC/zulip,rishig/zulip,brainwane/zulip,Galexrt/zulip,shubhamdhama/zulip,zulip/zulip,andersk/zulip,susansls/zulip,mohsenSy/zulip,grave-w-grave/zulip,kou/zulip,krtkmj/zulip,souravbadami/zulip,christi3k/zulip,jphilipsen05/zulip,PhilSk/zulip,mohsenSy/zulip,peguin40/zulip,isht3/zulip,rht/zulip,showell/zulip,peguin40/zulip,zulip/zulip,andersk/zulip,mohsenSy/zulip,joyhchen/zulip,kou/zulip,amanharitsh123/zulip,Galexrt/zulip,joyhchen/zulip,jackrzhang/zulip,Juanvulcano/zulip,aakash-cr7/zulip,samatdav/zulip,souravbadami/zulip,sonali0901/zulip,peguin40/zulip,susansls/zulip,verma-varsha/zulip,isht3/zulip,joyhchen/zulip,zulip/zulip,ryanbackman/zulip,reyha/zulip,SmartPeople/zulip,jrowan/zulip,paxapy/zulip,aakash-cr7/zulip,ryanbackman/zulip,dattatreya303/zulip,Vallher/zulip,rishig/zulip,verma-varsha/zulip,sonali0901/zulip,tommyip/zulip,jackrzhang/zulip,sharmaeklavya2/zulip,KingxBanana/zulip,jackrzhang/zulip,amanharitsh123/zulip,calvinleenyc/zulip,hackerkid/zulip,PhilSk/zulip,vaidap/zulip,souravbadami/zulip,showell/zulip,synicalsyntax/zulip,christi3k/zulip,Juanvulcano/zulip,mahim97/zulip,calvinleenyc/zulip,amyliu345/zulip,ahmadassaf/zulip,cosmicAsymmetry/zulip,SmartPeople/zulip,eeshangarg/zulip,vaidap/zulip,Galexrt/zulip,sonali0901/zulip,dhcrzf/zulip,joyhchen/zulip,jphilipsen05/zulip,dhcrzf/zulip,brainwane/zulip,jrowan/zulip,j831/zulip,vikas-parashar/zulip,Diptanshu8/zulip,jphilipsen05/zulip,hackerkid/zulip,AZtheAsian/zulip,vikas-parashar/zulip,TigorC/zulip,souravbadami/zulip,grave-w-grave/zulip,krtkmj/zulip,KingxBanana/zulip,isht3/zulip,kou/zulip,susansls/zulip,jackrzhang/zulip,peguin40/zulip,zacps/zulip,sharmaeklavya2/zulip,arpith/zulip,dhcrzf/zulip,krtkmj/zulip,mahim97/zulip,dhcrzf/zulip,umkay/zulip,punchagan/zulip,umkay/zulip,aakash-cr7/zulip,showell/zulip,jphilipsen05/zulip,umkay/zulip,eeshangarg/zulip,timabbott/zulip,niftynei/zulip,aakash-cr7/zulip,ryanbackman/zulip,blaze225/zulip,zacps/zulip,souravbadami/zulip,susansls/zulip,zacps/zulip,paxapy/zulip,zacps/zulip,Jianchun1/zulip,jphilipsen05/zulip,amanharitsh123/zulip,jackrzhang/zulip,jainayush975/zulip,tommyip/zulip,joyhchen/zulip,vabs22/zulip,showell/zulip,Diptanshu8/zulip,dhcrzf/zulip,jainayush975/zulip,calvinleenyc/zulip,vaidap/zulip,brockwhittaker/zulip,paxapy/zulip,verma-varsha/zulip,tommyip/zulip,synicalsyntax/zulip,cosmicAsymmetry/zulip,rht/zulip,PhilSk/zulip,punchagan/zulip,grave-w-grave/zulip,showell/zulip,AZtheAsian/zulip,jackrzhang/zulip,PhilSk/zulip,paxapy/zulip,sonali0901/zulip,verma-varsha/zulip,eeshangarg/zulip,brockwhittaker/zulip,Vallher/zulip,rishig/zulip,jainayush975/zulip,eeshangarg/zulip,sup95/zulip,umkay/zulip,andersk/zulip,JPJPJPOPOP/zulip,timabbott/zulip,Juanvulcano/zulip,sup95/zulip,peiwei/zulip,samatdav/zulip,vaidap/zulip,sup95/zulip,ahmadassaf/zulip,mohsenSy/zulip,rishig/zulip,sharmaeklavya2/zulip,j831/zulip,AZtheAsian/zulip,niftynei/zulip,dawran6/zulip,susansls/zulip,KingxBanana/zulip,arpith/zulip,Vallher/zulip,joyhchen/zulip,andersk/zulip,rht/zulip,Vallher/zulip,punchagan/zulip,amyliu345/zulip,grave-w-grave/zulip,niftynei/zulip,timabbott/zulip,shubhamdhama/zulip,shubhamdhama/zulip,zulip/zulip,blaze225/zulip,hackerkid/zulip,punchagan/zulip,SmartPeople/zulip,sup95/zulip,shubhamdhama/zulip,eeshangarg/zulip,ahmadassaf/zulip,JPJPJPOPOP/zulip,Juanvulcano/zulip,zulip/zulip,calvinleenyc/zulip,rht/zulip,brainwane/zulip,dhcrzf/zulip,TigorC/zulip,jrowan/zulip,rishig/zulip,tommyip/zulip,reyha/zulip,reyha/zulip,sup95/zulip,timabbott/zulip,blaze225/zulip,peguin40/zulip,synicalsyntax/zulip,JPJPJPOPOP/zulip,peiwei/zulip,tommyip/zulip,amyliu345/zulip,ahmadassaf/zulip,hackerkid/zulip,JPJPJPOPOP/zulip,vabs22/zulip,TigorC/zulip,umkay/zulip,grave-w-grave/zulip,vikas-parashar/zulip,peiwei/zulip,samatdav/zulip,peiwei/zulip,ahmadassaf/zulip,arpith/zulip,zulip/zulip,jrowan/zulip,JPJPJPOPOP/zulip,timabbott/zulip,dattatreya303/zulip,tommyip/zulip,PhilSk/zulip,jainayush975/zulip,JPJPJPOPOP/zulip,peiwei/zulip,vabs22/zulip,dawran6/zulip,kou/zulip,dattatreya303/zulip,brockwhittaker/zulip,rishig/zulip,sharmaeklavya2/zulip,synicalsyntax/zulip,isht3/zulip,zacps/zulip,peiwei/zulip,christi3k/zulip,peiwei/zulip