Fix location argument name for docs
It seems that the location argument name is wrong in the docs:
Probably a remnant of the pre v6.0.0 code. This should fix it.
@@ -324,7 +324,7 @@ class Parser:
:param argmap: Either a `marshmallow.Schema`, a `dict`
of argname -> `marshmallow.fields.Field` pairs, or a callable
which accepts a request and returns a `marshmallow.Schema`.
- :param str locations: Where on the request to load values.
+ :param str location: Where on the request to load values.
:param bool as_kwargs: Whether to insert arguments as keyword arguments.
:param callable validate: Validation function that receives the dictionary
of parsed arguments. If the function returns ``False``, the parser
