Use tornado.concurrent.Future instead of tornado.concurrent.TracebackFuture

tornado.concurrent.Future superceded tornado.concurrent.TracebackFuture
in Tornado 4.0. tornado.concurrent.TracebackFuture has been removed in
Tornado 5.x.

Author: WillSewell

pusher/tornado.py

@@ -10,7 +10,7 @@
 import tornado
 import tornado.httpclient
 
-from tornado.concurrent import TracebackFuture
+from tornado.concurrent import Future
 
 from pusher.http import process_response
 
@@ -30,7 +30,7 @@ def send_request(self, request):
         method = request.method
         data = request.body
         headers = {'Content-Type': 'application/json'}
-        future = TracebackFuture()
+        future = Future()
 
         def process_response_future(response):
             if response.exc_info() is not None: