Fix except syntax for python 3

Author: tarruda

neovim/msgpack_rpc/event_loop/asyncio.py

@@ -17,7 +17,7 @@
 try:
     # For python 3.4+, use the standard library module
     import asyncio
-except ImportError, SyntaxError:
+except (ImportError, SyntaxError):
     # Fallback to trollius
     import trollius as asyncio