Migrate to Travis trusty
Migrate to Travis trusty

Trusty has gcc 4.8, drop ubuntu-toolchain-r-test ppa

Fixes #794

abdonrd/polymer-starter-kit,Serious-Rage/poligomy,markovuksanovic/polymer-starter-kit,StartPolymer/polymer-starter-kit,abdonrd/polymer-starter-kit,anthonybrown/polymer-starter-kit,Ex-ante-Labs/shopper.ninja,StartPolymer/polymer-starter-kit-plus,Ex-ante-Labs/pivot-ahead,Serious-Rage/poligomy,StartPolymer/polymer-starter-kit,Ex-ante-Labs/pivot-ahead,anthonybrown/polymer-starter-kit,Ex-ante-Labs/shopper.ninja,markovuksanovic/polymer-starter-kit,lordoftheflies/mlm-portal,StartPolymer/polymer-starter-kit-plus,lordoftheflies/mlm-portal,Serious-Rage/poligomy,markovuksanovic/polymer-starter-kit,lordoftheflies/mlm-portal