Fix allow optional semicolon on regex

[preda-bogdan]

WordPress Theme check messages are sometimes inconsistent in formatting, :(semicolon) might be missing on some. This should better catch messages that don't always have a : present after the span.

The critical target is the span tag, the subsequent formatting should be optional.

@anhskohbo Let me know what you think, as at the moment we encountered some issues and this should solve those.

Thank you!