faq/tidb-faq: update out of date faqs (#3153)#3195

Merged

1 commit merged intopingcap:release-3.0from ti-srebot:release-3.0-80dda035eec5

Jul 7, 2020

+3-3

Commits on Jul 7, 2020

cherry pick pingcap#3153 to release-3.0

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