Fix typos

Author: nicholasbishop

server.rb

@@ -78,7 +78,7 @@ def get_payload_request(request)
     # Instantiate an Octokit client authenticated as a GitHub App.
     # GitHub App authentication requires that you construct a
     # JWT (https://jwt.io/introduction/) signed with the app's private key,
-    # so GitHub can be sure that it came from the app an not altererd by
+    # so GitHub can be sure that it came from the app and was not altered by
     # a malicious third party.
     def authenticate_app
       payload = {