Fixed .travis.yml to not use xdist for the hazardlib parallel tests
Fixed .travis.yml to not use xdist for the hazardlib parallel tests


Former-commit-id: 07c685e47dfbc89585aee07a339d875176e73ecf [formerly 07c685e47dfbc89585aee07a339d875176e73ecf [formerly bd7c8f074baa34b80e22540d12ed909d033f7091]]
Former-commit-id: ef3d545da57737d7bd03577a2c352ae3e9ea01ac
Former-commit-id: 52d002c1148a7b8c5c755c7c4ad05e76b5c23b4c
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine