TEST: updated travis script to install requirements
TEST: updated travis script to install requirements

Former-commit-id: 19565a2638a353fcbc9b519b8c946f5d86dcaefa
Former-commit-id: dee4beb5195155c82371a6bd9a8ab9a97f6ca58e
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox