Make Comparer.is_match property work ...

[webartifex]

... for an errors dictionary full of
inspectors without any errors, for example:

{
    'columns': {},
    'primary_keys': {},
    'foreign_keys': {},
    'indexes': {},
    'unique_constraints': {},
    'check_constraints': {},
}

[webartifex]

The above example show an example where the two databases compared are identical.

The current not self.errors check in the is_match property gives the wrong answer: It thinks the two databases are not identical.

I did not check when this bug was introduced (must be v1 though) nor did I run the test suite. So, maybe some test cases need adjustment too.

[gianchub]

Much appreciated @webartifex :)
Will fix in #29
Will go out today in v1.0.4.

[webartifex]

Your solution is way nicer :)