Deprecation warnings

[esschul]

When invoking getFunctionMock I am getting the following deprecation warnings.

• MockBuilder::addMethods() is deprecated and will be removed in PHPUnit 12 without replacement.
• MockBuilder::getMockForAbstractClass() is deprecated and will be removed in PHPUnit 12 without replacement.

[michalbundyra]

@esschul thanks, see: #70

[esschul]

Thanks!

[michalbundyra]

Maybe lets leave it open, as it will be easier for others to spot the issue. Still if someone will provide the fix now I can accept it, but I am not going to work on it separately before we see PHPUnit 12.

Thanks

[crocodele]

@michalbundyra, could you please have a look at the linked draft PR and let me know what you think? Thanks!

[michalbundyra]

Done in #75, thanks @crocodele !