travis: Remove unnecessary nvm install step.
travis: Remove unnecessary nvm install step.

This was needed before Zulip switched to using a pinned node version.

punchagan/zulip,tommyip/zulip,jackrzhang/zulip,brainwane/zulip,amanharitsh123/zulip,verma-varsha/zulip,brockwhittaker/zulip,verma-varsha/zulip,andersk/zulip,mahim97/zulip,shubhamdhama/zulip,kou/zulip,Galexrt/zulip,andersk/zulip,zulip/zulip,punchagan/zulip,mahim97/zulip,tommyip/zulip,synicalsyntax/zulip,shubhamdhama/zulip,hackerkid/zulip,timabbott/zulip,rishig/zulip,mahim97/zulip,kou/zulip,shubhamdhama/zulip,kou/zulip,brainwane/zulip,punchagan/zulip,kou/zulip,rht/zulip,amanharitsh123/zulip,shubhamdhama/zulip,vabs22/zulip,jackrzhang/zulip,eeshangarg/zulip,dhcrzf/zulip,andersk/zulip,Galexrt/zulip,dhcrzf/zulip,rishig/zulip,amanharitsh123/zulip,vaidap/zulip,rishig/zulip,hackerkid/zulip,jackrzhang/zulip,jrowan/zulip,jrowan/zulip,showell/zulip,brockwhittaker/zulip,synicalsyntax/zulip,mahim97/zulip,timabbott/zulip,andersk/zulip,synicalsyntax/zulip,rishig/zulip,amanharitsh123/zulip,eeshangarg/zulip,tommyip/zulip,synicalsyntax/zulip,dhcrzf/zulip,Galexrt/zulip,Galexrt/zulip,kou/zulip,brockwhittaker/zulip,punchagan/zulip,tommyip/zulip,zulip/zulip,amanharitsh123/zulip,rht/zulip,rishig/zulip,hackerkid/zulip,andersk/zulip,eeshangarg/zulip,vaidap/zulip,tommyip/zulip,showell/zulip,zulip/zulip,tommyip/zulip,brockwhittaker/zulip,dhcrzf/zulip,kou/zulip,jrowan/zulip,punchagan/zulip,eeshangarg/zulip,jackrzhang/zulip,jackrzhang/zulip,shubhamdhama/zulip,rht/zulip,hackerkid/zulip,showell/zulip,vabs22/zulip,showell/zulip,rht/zulip,dhcrzf/zulip,rht/zulip,jrowan/zulip,verma-varsha/zulip,punchagan/zulip,shubhamdhama/zulip,punchagan/zulip,rht/zulip,rishig/zulip,Galexrt/zulip,vabs22/zulip,hackerkid/zulip,synicalsyntax/zulip,synicalsyntax/zulip,jrowan/zulip,brainwane/zulip,vaidap/zulip,amanharitsh123/zulip,timabbott/zulip,showell/zulip,eeshangarg/zulip,eeshangarg/zulip,zulip/zulip,brainwane/zulip,vabs22/zulip,tommyip/zulip,brockwhittaker/zulip,brainwane/zulip,timabbott/zulip,zulip/zulip,verma-varsha/zulip,mahim97/zulip,verma-varsha/zulip,vabs22/zulip,vabs22/zulip,mahim97/zulip,showell/zulip,timabbott/zulip,Galexrt/zulip,shubhamdhama/zulip,jackrzhang/zulip,zulip/zulip,rht/zulip,eeshangarg/zulip,synicalsyntax/zulip,rishig/zulip,vaidap/zulip,andersk/zulip,kou/zulip,dhcrzf/zulip,brainwane/zulip,brockwhittaker/zulip,brainwane/zulip,jackrzhang/zulip,vaidap/zulip,verma-varsha/zulip,vaidap/zulip,hackerkid/zulip,dhcrzf/zulip,Galexrt/zulip,hackerkid/zulip,andersk/zulip,showell/zulip,zulip/zulip,timabbott/zulip,jrowan/zulip,timabbott/zulip