Fix a typo in faq.md
Fix a typo in faq.md

Former-commit-id: ad1298cd7acebc147dcd35595d184d2841391fd2 [formerly 4429f9e3ed1006a827588d956e214a495f6702fb]
Former-commit-id: 698f8f5248eccb6841e9917137fcdb36e049f51f
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine