blame: Linkify servo PR in commit message headers.
blame: Linkify servo PR in commit message headers.

While at it, also avoid creating a regex each time that function is called.

bill-mccloskey/searchfox,bill-mccloskey/mozsearch,bill-mccloskey/mozsearch,bill-mccloskey/searchfox,bill-mccloskey/searchfox,bill-mccloskey/searchfox,bill-mccloskey/mozsearch,bill-mccloskey/mozsearch,bill-mccloskey/searchfox,bill-mccloskey/mozsearch,bill-mccloskey/searchfox,bill-mccloskey/mozsearch