Fix a typo in faq.md [skip ci]
Fix a typo in faq.md [skip ci]

Former-commit-id: 7df4f59cda28f80c1ce35d0a69041e9a51bdb887 [formerly 123002035ba8767de72c1ada1b4f1ea3a2e0cf9e]
Former-commit-id: 1154de4874c9ae7cb76efbf9c7cf5283bea43580
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine