fix(.travis.yml): attempt to solve build problem by adding gcc-4.8 ppa
fix(.travis.yml): attempt to solve build problem by adding gcc-4.8 ppa

Hodapp87/cs6460_project,cjmazey/fork_leanprover_tutorial,Hodapp87/cs6460_project,Hodapp87/cs6460_project,avigad/tutorial,cjmazey/fork_leanprover_tutorial,soonhokong/lean-tutorial,leanprover/tutorial,fpvandoorn/tutorial,fpvandoorn/tutorial,fpvandoorn/tutorial,leanprover/tutorial,soonhokong/lean-tutorial,cjmazey/fork_leanprover_tutorial,leanprover/tutorial,avigad/tutorial,avigad/tutorial,soonhokong/lean-tutorial