Override travis install to always use npm (#994)
Override travis install to always use npm (#994)

* avoid yarn default for now
cedricbellet/lighthouse,mixed/lighthouse,wardpeet/lighthouse,ev1stensberg/lighthouse,arturmiz/lighthouse,cedricbellet/lighthouse,mixed/lighthouse,umaar/lighthouse,wardpeet/lighthouse,cedricbellet/lighthouse,cedricbellet/lighthouse,deepanjanroy/lighthouse,arturmiz/lighthouse,tommycli/lighthouse,tommycli/lighthouse,tommycli/lighthouse,deepanjanroy/lighthouse,ev1stensberg/lighthouse,GoogleChrome/lighthouse,mixed/lighthouse,GoogleChrome/lighthouse,umaar/lighthouse,umaar/lighthouse,ev1stensberg/lighthouse,deepanjanroy/lighthouse,GoogleChrome/lighthouse,wardpeet/lighthouse,GoogleChrome/lighthouse,ev1stensberg/lighthouse,tommycli/lighthouse,mixed/lighthouse,wardpeet/lighthouse,wardpeet/lighthouse,tkadlec/lighthouse,arturmiz/lighthouse,tommycli/lighthouse,cedricbellet/lighthouse,arturmiz/lighthouse,tkadlec/lighthouse,arturmiz/lighthouse,GoogleChrome/lighthouse,tkadlec/lighthouse,umaar/lighthouse,deepanjanroy/lighthouse,tkadlec/lighthouse,deepanjanroy/lighthouse