Block amend commits

Amend commits are a new type of fixup commits recently added by git.
They allow you to fully replace the commit message of the commit you are
amending. Since they semantically the same as fixup commits, we
similarly don't want to ever merge them into our master branch.

Author: pieterdd

github-webhooks/validators/fixupCommits.js

@@ -15,7 +15,7 @@ const FixupValidator = function() {
             .then((commits) => {
                 const messages = commits.map((a) => a.commit.message);
                 const fixups = messages
-                    .filter((message) => message.startsWith('fixup!') || message.startsWith('squash!'));
+                    .filter((message) => message.startsWith('fixup!') || message.startsWith('squash!') || message.startsWith('amend!'));
                 let state = self.gitHubClient.COMMITSTATUS.SUCCESS;
                 let description = 'no fixups found, you\'re good to go!';
                 if (fixups.length > 0) {