Summary: was using `[foo|bar]` to match `foo` or `bar` instead of `\\(foo\\|bar\\)` (ocaml/emacs regexes are the worst). this meant that the "site" part of FlowFixMe and FlowIssue suppression comments were basically not working, so a suppression in one site suppressed the other incorrectly.

Reviewed By: jbrown215

Differential Revision: D10365477

fbshipit-source-id: 1188c7378b5e6fd3090b27c1aa54480efdd09250