Fixed #12603 -- Corrected typo in m2m signals docs. Thanks to hvdklauw for the report.

    ``sender``

        The intermediate model class describing the :class:`ManyToManyField`.

        This class is automatically created when a many-to-many field is

        defined; it you can access it using the ``through`` attribute on the

        defined; you can access it using the ``through`` attribute on the

        many-to-many field.

    ``instance``