Cache node_modules on travis
Cache node_modules on travis

We disabled this because of intermittent build errors, but if it's resolved, it will speed up the builds considerably.

alpha721/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,sejalkhatri/WikiEduDashboard,Wowu/WikiEduDashboard,MusikAnimal/WikiEduDashboard,majakomel/WikiEduDashboard,majakomel/WikiEduDashboard,Wowu/WikiEduDashboard,Wowu/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,feelfreelinux/WikiEduDashboard,sejalkhatri/WikiEduDashboard,KarmaHater/WikiEduDashboard,MusikAnimal/WikiEduDashboard,KarmaHater/WikiEduDashboard,majakomel/WikiEduDashboard,KarmaHater/WikiEduDashboard,alpha721/WikiEduDashboard,MusikAnimal/WikiEduDashboard,sejalkhatri/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,feelfreelinux/WikiEduDashboard,feelfreelinux/WikiEduDashboard,alpha721/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,alpha721/WikiEduDashboard,sejalkhatri/WikiEduDashboard,MusikAnimal/WikiEduDashboard,feelfreelinux/WikiEduDashboard,majakomel/WikiEduDashboard,sejalkhatri/WikiEduDashboard,KarmaHater/WikiEduDashboard,Wowu/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard