test: Fix regression in tls test

Undefined reference, introduced by a77c29a.

test/simple/test-tls-over-http-tunnel.js

@@ -162,7 +162,7 @@ proxy.listen(proxyPort, function() {
         proxy.close();
         server.close();
       });
-    }).on('error', function() {
+    }).on('error', function(er) {
       // We're ok with getting ECONNRESET in this test, but it's
       // timing-dependent, and thus unreliable. Any other errors
       // are just failures, though.