Travis: usage of container-based infrastructure
Travis: usage of container-based infrastructure

Signed-off-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

glennmatthews/pep257,bagelbits/pep257,PyCQA/pydocstyle,jayvdb/pep257,13steinj/pep257,farmersez/pydocstyle,jbeezley/pep257,Nurdok/pydocstyle,codehs/pep257,Nurdok/pep257,jmullan/pep257,pombredanne/pep257,GreenSteam/pep257,tescalada/pydocstyle