event_loop/asyncio.py: Attach loop to child watcher (#241)

Closes #238

Author: heliomeiralins

neovim/msgpack_rpc/event_loop/asyncio.py

@@ -93,6 +93,8 @@ def _connect_stdio(self):
         self._loop.run_until_complete(coroutine)
 
     def _connect_child(self, argv):
+        self._child_watcher = asyncio.get_child_watcher()
+        self._child_watcher.attach_loop(self._loop)
         coroutine = self._loop.subprocess_exec(self._fact, *argv)
         self._loop.run_until_complete(coroutine)