Run the demos in parallel in .travis.yml [skip CI]
Run the demos in parallel in .travis.yml [skip CI]


Former-commit-id: c3bd524fb59b17d50cb6a387a9b34a6aeb93edc4 [formerly fe2b7f46cf2ed23a860db60f772cedf16c6e4540]
Former-commit-id: 58c809c53980f5cfa00df39d8ebed7fc5127a003
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine