travis: Remove npm cache in prod installation.
travis: Remove npm cache in prod installation.

With this change in place, we would have been able to catch the bug
fixed in the last commit in CI.

jrowan/zulip,vabs22/zulip,niftynei/zulip,Galexrt/zulip,SmartPeople/zulip,j831/zulip,amyliu345/zulip,JPJPJPOPOP/zulip,jphilipsen05/zulip,ryanbackman/zulip,verma-varsha/zulip,aakash-cr7/zulip,j831/zulip,susansls/zulip,arpith/zulip,hackerkid/zulip,mahim97/zulip,brainwane/zulip,christi3k/zulip,dhcrzf/zulip,isht3/zulip,aakash-cr7/zulip,samatdav/zulip,jackrzhang/zulip,AZtheAsian/zulip,shubhamdhama/zulip,vaidap/zulip,vabs22/zulip,isht3/zulip,brockwhittaker/zulip,niftynei/zulip,ryanbackman/zulip,Diptanshu8/zulip,sharmaeklavya2/zulip,zacps/zulip,punchagan/zulip,Galexrt/zulip,dawran6/zulip,amanharitsh123/zulip,zacps/zulip,amanharitsh123/zulip,PhilSk/zulip,rht/zulip,arpith/zulip,Galexrt/zulip,kou/zulip,punchagan/zulip,brockwhittaker/zulip,showell/zulip,mahim97/zulip,brockwhittaker/zulip,rht/zulip,jrowan/zulip,SmartPeople/zulip,Diptanshu8/zulip,showell/zulip,dhcrzf/zulip,Juanvulcano/zulip,brockwhittaker/zulip,dattatreya303/zulip,tommyip/zulip,eeshangarg/zulip,christi3k/zulip,jainayush975/zulip,amanharitsh123/zulip,punchagan/zulip,tommyip/zulip,sharmaeklavya2/zulip,niftynei/zulip,punchagan/zulip,joyhchen/zulip,showell/zulip,AZtheAsian/zulip,SmartPeople/zulip,dawran6/zulip,timabbott/zulip,blaze225/zulip,Galexrt/zulip,KingxBanana/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,Diptanshu8/zulip,Diptanshu8/zulip,souravbadami/zulip,jainayush975/zulip,kou/zulip,timabbott/zulip,dhcrzf/zulip,vabs22/zulip,timabbott/zulip,hackerkid/zulip,amyliu345/zulip,zulip/zulip,TigorC/zulip,AZtheAsian/zulip,amanharitsh123/zulip,rishig/zulip,Juanvulcano/zulip,TigorC/zulip,aakash-cr7/zulip,jackrzhang/zulip,sharmaeklavya2/zulip,tommyip/zulip,zacps/zulip,shubhamdhama/zulip,susansls/zulip,sharmaeklavya2/zulip,KingxBanana/zulip,sonali0901/zulip,TigorC/zulip,hackerkid/zulip,dawran6/zulip,dhcrzf/zulip,dattatreya303/zulip,ryanbackman/zulip,verma-varsha/zulip,shubhamdhama/zulip,hackerkid/zulip,brockwhittaker/zulip,zacps/zulip,KingxBanana/zulip,brainwane/zulip,vabs22/zulip,amyliu345/zulip,brainwane/zulip,susansls/zulip,jrowan/zulip,zulip/zulip,mahim97/zulip,jphilipsen05/zulip,samatdav/zulip,timabbott/zulip,ryanbackman/zulip,rishig/zulip,eeshangarg/zulip,dawran6/zulip,blaze225/zulip,timabbott/zulip,isht3/zulip,synicalsyntax/zulip,brainwane/zulip,vabs22/zulip,cosmicAsymmetry/zulip,brainwane/zulip,sonali0901/zulip,christi3k/zulip,shubhamdhama/zulip,aakash-cr7/zulip,eeshangarg/zulip,KingxBanana/zulip,cosmicAsymmetry/zulip,zulip/zulip,JPJPJPOPOP/zulip,blaze225/zulip,brockwhittaker/zulip,j831/zulip,jainayush975/zulip,kou/zulip,AZtheAsian/zulip,niftynei/zulip,amanharitsh123/zulip,amyliu345/zulip,sonali0901/zulip,amyliu345/zulip,dawran6/zulip,dattatreya303/zulip,SmartPeople/zulip,christi3k/zulip,dhcrzf/zulip,kou/zulip,eeshangarg/zulip,dattatreya303/zulip,timabbott/zulip,andersk/zulip,tommyip/zulip,Diptanshu8/zulip,AZtheAsian/zulip,JPJPJPOPOP/zulip,mahim97/zulip,kou/zulip,andersk/zulip,dhcrzf/zulip,sharmaeklavya2/zulip,isht3/zulip,jrowan/zulip,dawran6/zulip,Diptanshu8/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,jackrzhang/zulip,verma-varsha/zulip,Juanvulcano/zulip,tommyip/zulip,sonali0901/zulip,jphilipsen05/zulip,rishig/zulip,vaidap/zulip,souravbadami/zulip,Juanvulcano/zulip,jainayush975/zulip,rishig/zulip,showell/zulip,j831/zulip,rht/zulip,isht3/zulip,PhilSk/zulip,amyliu345/zulip,arpith/zulip,arpith/zulip,arpith/zulip,rht/zulip,joyhchen/zulip,SmartPeople/zulip,blaze225/zulip,tommyip/zulip,rishig/zulip,shubhamdhama/zulip,vaidap/zulip,susansls/zulip,TigorC/zulip,tommyip/zulip,Galexrt/zulip,zulip/zulip,JPJPJPOPOP/zulip,eeshangarg/zulip,jphilipsen05/zulip,cosmicAsymmetry/zulip,susansls/zulip,rht/zulip,christi3k/zulip,shubhamdhama/zulip,showell/zulip,sharmaeklavya2/zulip,punchagan/zulip,Juanvulcano/zulip,jackrzhang/zulip,hackerkid/zulip,andersk/zulip,shubhamdhama/zulip,blaze225/zulip,verma-varsha/zulip,brainwane/zulip,ryanbackman/zulip,timabbott/zulip,brainwane/zulip,samatdav/zulip,souravbadami/zulip,souravbadami/zulip,christi3k/zulip,souravbadami/zulip,mahim97/zulip,jphilipsen05/zulip,jphilipsen05/zulip,andersk/zulip,eeshangarg/zulip,joyhchen/zulip,showell/zulip,cosmicAsymmetry/zulip,zacps/zulip,cosmicAsymmetry/zulip,j831/zulip,andersk/zulip,zulip/zulip,joyhchen/zulip,PhilSk/zulip,samatdav/zulip,Galexrt/zulip,jainayush975/zulip,dattatreya303/zulip,aakash-cr7/zulip,niftynei/zulip,eeshangarg/zulip,dhcrzf/zulip,PhilSk/zulip,synicalsyntax/zulip,synicalsyntax/zulip,samatdav/zulip,kou/zulip,amanharitsh123/zulip,KingxBanana/zulip,synicalsyntax/zulip,Galexrt/zulip,isht3/zulip,arpith/zulip,sonali0901/zulip,samatdav/zulip,ryanbackman/zulip,SmartPeople/zulip,KingxBanana/zulip,kou/zulip,mahim97/zulip,punchagan/zulip,Juanvulcano/zulip,souravbadami/zulip,joyhchen/zulip,JPJPJPOPOP/zulip,jrowan/zulip,cosmicAsymmetry/zulip,rht/zulip,blaze225/zulip,PhilSk/zulip,jackrzhang/zulip,sonali0901/zulip,jrowan/zulip,showell/zulip,dattatreya303/zulip,hackerkid/zulip,rht/zulip,synicalsyntax/zulip,vaidap/zulip,rishig/zulip,jackrzhang/zulip,synicalsyntax/zulip,PhilSk/zulip,JPJPJPOPOP/zulip,aakash-cr7/zulip,vaidap/zulip,vabs22/zulip,zacps/zulip,AZtheAsian/zulip,verma-varsha/zulip,verma-varsha/zulip,joyhchen/zulip,jainayush975/zulip,niftynei/zulip,TigorC/zulip,TigorC/zulip,susansls/zulip,jackrzhang/zulip,rishig/zulip,j831/zulip,vaidap/zulip,synicalsyntax/zulip