Force travis to use npm 2.x.
Force travis to use npm 2.x.

jeffbski/joi,robertherber/joi-extended,tpiecora/joi,cesarmarinhorj/joi,ck-lee/joi,danielb2/joi,rmoorman/joi,lloydbenson/joi,bananaoomarang/joi,davidbenko9/joi,pikselpalette/joi,thethanghn/react-native-joi,geminiyellow/joi,opyate/joi,naitsric/joi,jagoda/joi