[mediacapture-main] Merged Pull Request: Travis improvements and changes for latest espec

vivienlacourba has just merged pull request 347 for 
https://github.com/w3c/mediacapture-main:

== Travis improvements and changes for latest espec ==
Those changes are making the build configuration of the 
mediacapture-main and webrtc-pc repos similar.

See https://github.com/w3c/mediacapture-main/pull/347