call req.path() if a function. restify compat, fixes pinojs#88

in pinojs#29 we preferred req.path, because req.url would throw in hapi if the path was invalid. in restify though, req.path is a function, and this change made the url no longer log. check req.path to see if it is a function, and invoke it if it is.

lib/req.js

@@ -73,9 +73,12 @@ function reqSerializer (req) {
     _req.url = req.originalUrl
     _req.query = req.query
     _req.params = req.params
+  } else if (req.path) {
+    // req.path is to make hapi safe with invalid paths.  req.path() is for restify compat.
+    _req.url = typeof req.path === 'function' ? req.path() : req.path
   } else {
     // req.url.path is  for hapi compat.
-    _req.url = req.path || (req.url ? (req.url.path || req.url) : undefined)
+    _req.url = req.url ? (req.url.path || req.url) : undefined
   }
   _req.headers = req.headers
   _req.remoteAddress = connection && connection.remoteAddress