protect execution_count from longs returned by json

IPython/frontend/zmqterminal/interactiveshell.py

@@ -101,7 +101,7 b' class ZMQTerminalInteractiveShell(TerminalInteractiveShell):'
                 for frame in msg["content"]["traceback"]:
                     print(frame, file=io.stderr)
             
-            self.execution_count = msg["content"]["execution_count"] + 1
+            self.execution_count = int(msg["content"]["execution_count"] + 1)
 
 
     def handle_iopub(self):