Validating a Mapping that isn't a dict fails

[thanatos]

This is essentially the same issue as #125; it appears maybe this feature is now broken?

I, like #125, am attempting to validate an aiohttp request query arguments, which isn't a dict, but is a Mapping.

However, voluptuous requires a dict, as can be seen here; I see this in my stack trace:

Traceback (most recent call last):
  File "…/lib/python3.6/site-packages/voluptuous/schema_builder.py", line 221, in __call__
    return self._compiled([], data)
  File "…/lib/python3.6/site-packages/voluptuous/schema_builder.py", line 504, in validate_dict
    raise er.DictInvalid('expected a dictionary', path)
voluptuous.error.DictInvalid: expected a dictionary

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "…/lib/python3.6/site-packages/aiohttp/web_protocol.py", line 422, in start
    resp = yield from self._request_handler(request)
  File "…/lib/python3.6/site-packages/aiohttp/web.py", line 306, in _handle
    resp = yield from handler(request)
  File "…/__main__.py", line 32, in wrapper
    json_data = await func(*args, **kwargs)
  File "…/__main__.py", line 88, in foo
    validated_qargs = _SCHEMA(request.query)
  File "…/lib/python3.6/site-packages/voluptuous/schema_builder.py", line 225, in __call__
    raise er.MultipleInvalid([e])
voluptuous.error.MultipleInvalid: expected a dictionary

I think it's as simple as changing that dict to Mapping?