Add Python 3.7 to travis
Add Python 3.7 to travis


Former-commit-id: b0ae44b27bdf8f006a4d90318ee838db6ed00a57 [formerly b0ae44b27bdf8f006a4d90318ee838db6ed00a57 [formerly b668b5629725e0cdad134dfa3a56f023da33fb48]]
Former-commit-id: ac0bc50e5a9e3553b0b9ac952a23324fac7ffea8
Former-commit-id: 2c448567aa02e59c76662125e7484d6009f5af36
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine