Fix a typo in doc [skip ci]
Fix a typo in doc [skip ci]


Former-commit-id: 27c1e259d04ccda8a495ec442b45893b34fad624 [formerly eb0a5275232bd5ff6cc5863314391696c59a39e1]
Former-commit-id: b9577c7e2e8dad8142b15932ee2d6d762022aeb5
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine