[enh] Migrating Travis CI from legacy to container-based infrastructure
[enh] Migrating Travis CI from legacy to container-based infrastructure

This patch should speedup testing with Travis CI using caching and
container-based infrastructure.

source:
- http://docs.travis-ci.com/user/migrating-from-legacy/
- http://docs.travis-ci.com/user/caching/

asciimoo/searx,asciimoo/searx,pointhi/searx,dzc34/searx,asciimoo/searx,dzc34/searx,jibe-b/searx,PwnArt1st/searx,potato/searx,PwnArt1st/searx,gugod/searx,GreenLunar/searx,dalf/searx,dzc34/searx,jibe-b/searx,asciimoo/searx,dalf/searx,dalf/searx,jcherqui/searx,gugod/searx,matejc/searx,misnyo/searx,jibe-b/searx,GreenLunar/searx,potato/searx,matejc/searx,jcherqui/searx,GreenLunar/searx,misnyo/searx,potato/searx,matejc/searx,potato/searx,pointhi/searx,matejc/searx,pointhi/searx,dalf/searx,jcherqui/searx,GreenLunar/searx,PwnArt1st/searx,jcherqui/searx,PwnArt1st/searx,gugod/searx,dzc34/searx,pointhi/searx,misnyo/searx,gugod/searx,jibe-b/searx,misnyo/searx