v0.15.0

This release contains an update to re-evaluate the skip conditions (e.g. PR state, required labels) on each retry of the merge mechanism. By doing so, a running automerge job is now able to react to changes that have occurred since it was triggered; for example, if the PR is closed or if a merge-blocking label is added to the PR, the next time the running automerge job polls for "mergeability", it will encounter a failure condition and cease its polling.