travis: Fix zulip-npm-cache in Travis CI.
travis: Fix zulip-npm-cache in Travis CI.

Apparently, when we migrated local development to use the
zulip-npm-cache structure, we failed to update the .travis.yml file
with the appropriate directory (and instead just uploaded a
node_modules symlink).

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