fix: properly assign options when creating the transport

The query attribute was overwritten, due to the order of arguments in
the assignment. The bug was introduced in the refactor (5f47a50).

lib/socket.js

@@ -121,18 +121,18 @@ class Socket extends Emitter {
     if (this.id) query.sid = this.id;
 
     const opts = Object.assign(
+      {},
+      this.opts.transportOptions[name],
+      this.opts,
       {
         query,
         socket: this,
         hostname: this.hostname,
         secure: this.secure,
         port: this.port
-      },
-      this.opts.transportOptions[name],
-      this.opts
+      }
     );
 
-    // console.log(opts);
     debug("options: %j", opts);
 
     return new transports[name](opts);

lib/transports/polling-xhr.js

@@ -102,6 +102,7 @@ class XHR extends Polling {
     req.on("error", function(err) {
       self.onError("xhr poll error", err);
     });
+    this.pollXhr = req;
   }
 }