http: describe parse err in debug output

PR-URL: https://github.com/nodejs/node/pull/13206
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

lib/_http_server.js

@@ -462,7 +462,7 @@ function socketOnError(e) {
 
 function onParserExecuteCommon(server, socket, parser, state, ret, d) {
   if (ret instanceof Error) {
-    debug('parse error');
+    debug('parse error', ret);
     socketOnError.call(socket, ret);
   } else if (parser.incoming && parser.incoming.upgrade) {
     // Upgrade or CONNECT