Update Nvim error handling

Now errors sent from Nvim are [code, message] arrays, this adapts the error
handling code to account for that.

Author: tarruda

neovim/client.py

@@ -97,7 +97,8 @@ def rpc_request(self, method, args, expected_type=None, decode_str=None):
             err, result = self.rpc_blocking_request(method, args, decode_str=decode_str)
 
         if err:
-            raise VimError(err)
+            info("'Received error of type '%d'", err[0])
+            raise VimError(err[1])
 
         return result