log the IP address as seen by Express, if available

For `remote-addr`, the logging middleware should use `req.ip`, the IP
address seen by Express. This is especially useful when behind a proxy
with the Express “trust proxy” option. If `req.ip` is not enabled,
fallback to the traditional method.

lib/middleware/logger.js

@@ -299,7 +299,7 @@ exports.token('referrer', function(req){
  */
 
 exports.token('remote-addr', function(req){
-  return req.socket && (req.socket.remoteAddress || (req.socket.socket && req.socket.socket.remoteAddress));
+  return req.ip || req.socket && (req.socket.remoteAddress || (req.socket.socket && req.socket.socket.remoteAddress));
 });
 
 /**