fix for 'ignores' not working

Hi,

Your cobertur plugin is really good and I like the style, it's simple and readable.

But, I found the 'ignores' is not working, and then I tried to understand the code, and made a fix.

After this fix, we can use the same way like 'includes' and 'excludes' to config 'ignores' instead of regex, maybe this way is more consistent?

Looking forward to your opinion.

Cheers,
David