Don't use BaseException.message @equalsraf

BaseException.message was only available in Python 2.5:
https://www.python.org/dev/peps/pep-0352/#retracted-ideas

This was patch was proposed in neovim/neovim #4253:
neovim/neovim#4253 (comment)

This hides any errors behind an AttributeError:
AttributeError: 'OSError' object has no attribute 'message'

Author: maxwell-k

neovim/msgpack_rpc/event_loop/asyncio.py

@@ -44,7 +44,7 @@ def connection_made(self, transport):
 
     def connection_lost(self, exc):
         """Used to signal `asyncio.Protocol` of a lost connection."""
-        self._on_error(exc.message if exc else 'EOF')
+        self._on_error(exc.args[0] if exc else 'EOF')
 
     def data_received(self, data):
         """Used to signal `asyncio.Protocol` of incoming data."""
@@ -55,7 +55,7 @@ def data_received(self, data):
 
     def pipe_connection_lost(self, fd, exc):
         """Used to signal `asyncio.SubprocessProtocol` of a lost connection."""
-        self._on_error(exc.message if exc else 'EOF')
+        self._on_error(exc.args[0] if exc else 'EOF')
 
     def pipe_data_received(self, fd, data):
         """Used to signal `asyncio.SubprocessProtocol` of incoming data."""