Remove guard-yard
Make spec syntax 1.8.7 compatible
Make OTP delivery regex 1.8.7 compatible
Backports, spec tweaks for pubsubhubbub compat for 1.8.7
1.8.7 compat for Releases
Run CI on 1.8.7
Merge pull request #317 from octokit/one-eight-seven

Restore 1.8.7 compatibility