Make changelog build commits not trigger a travis build

There is no reason to build tests on these as they are automated
and not often checked, plus, they do not modify code and the
changelog yaml should already be verified when it was merged

[ci skip]

tools/github_webhook_processor.php

@@ -262,7 +262,7 @@ function checkchangelog($payload, $merge = false) {
 	}
 	$content = array (
 		'branch' 	=> $payload['pull_request']['base']['ref'],
-		'message' 	=> 'Automatic changelog generation for PR #'.$payload['pull_request']['number'],
+		'message' 	=> 'Automatic changelog generation for PR #'.$payload['pull_request']['number'].'[ci skip]',
 		'content' 	=> base64_encode($file)
 	);
 	$scontext = array('http' => array(