Added Gogs (SHA256) signature support

[realJoshByrnes]

A minor addition of supporting Gogs headers (sha256).

I personally use Gitea, which is a fork of gogs. Gitea sends both Gogs and Gitea headers.

Headers are shown below for informational purposes.

X-GitHub-Delivery: 65ba5b3a-0728-490e-b724-6f312be28682
X-GitHub-Event: push
X-Gitea-Delivery: 65ba5b3a-0728-490e-b724-6f312be28682
X-Gitea-Event: push
X-Gitea-Signature: 4f047f14202020d8667e4644deb0fbd80fc5a2e35c3784f10b91e501affe672c
X-Gogs-Delivery: 65ba5b3a-0728-490e-b724-6f312be28682
X-Gogs-Event: push
X-Gogs-Signature: 4f047f14202020d8667e4644deb0fbd80fc5a2e35c3784f10b91e501affe672c

An automatic merge can not be performed due to some code changes on the desaroger/pm2-hooks repo.