fix(travis-ci): Speed up the build for TravisCI
fix(travis-ci): Speed up the build for TravisCI

This commit speeds up the builds by upto 3 times than the current.
It uses npm 3 over npm 2 (travis default), and caches the
dependencies.

This is okay, because our prime two testing areas are, linting and
tests for the challenges.

NOTE: The speed up should happen from the second build,
as it will take atleast one build to cache the dependencies.

raisedadead/FreeCodeCamp,MiloATH/FreeCodeCamp,codeman869/FreeCodeCamp,techstonia/FreeCodeCamp,BhaveshSGupta/FreeCodeCamp,no-stack-dub-sack/freeCodeCamp,MiloATH/FreeCodeCamp,FreeCodeCampQuito/FreeCodeCamp,jonathanihm/freeCodeCamp,DusanSacha/FreeCodeCamp,matthew-t-smith/freeCodeCamp,BhaveshSGupta/FreeCodeCamp,otavioarc/freeCodeCamp,BerkeleyTrue/FreeCodeCamp,sakthik26/FreeCodeCamp,TheeMattOliver/FreeCodeCamp,systimotic/FreeCodeCamp,TheeMattOliver/FreeCodeCamp,BrendanSweeny/FreeCodeCamp,techstonia/FreeCodeCamp,Munsterberg/freecodecamp,tmashuang/FreeCodeCamp,otavioarc/freeCodeCamp,1111113j8Pussy420/https-github.com-raisedadead-freeCodeCamp,Munsterberg/freecodecamp,FreeCodeCampQuito/FreeCodeCamp,jonathanihm/freeCodeCamp,tmashuang/FreeCodeCamp,codeman869/FreeCodeCamp,BerkeleyTrue/FreeCodeCamp,BhaveshSGupta/FreeCodeCamp,HKuz/FreeCodeCamp,sakthik26/FreeCodeCamp,BrendanSweeny/FreeCodeCamp,HKuz/FreeCodeCamp,1111113j8Pussy420/https-github.com-raisedadead-freeCodeCamp,systimotic/FreeCodeCamp,no-stack-dub-sack/freeCodeCamp,FreeCodeCamp/FreeCodeCamp,FreeCodeCamp/FreeCodeCamp,pahosler/freecodecamp,matthew-t-smith/freeCodeCamp,DusanSacha/FreeCodeCamp,pahosler/freecodecamp,raisedadead/FreeCodeCamp