Fix bug: dashes in theme names could break SCSS build.

[demiankatz]

@dltj reported that SCSS did not compile correctly when extending a theme containing a dash character. This PR fixes the problem. It's possible that an even broader regex would be more appropriate here, but I wanted to keep my fix targeted for starters.

[djones-scu-edu]

Shouldn't the dash come first in the character class or be escaped?

[demiankatz]

Thanks, @djones-scu-edu. For whatever reason, it works correctly without escaping the dash (maybe a lone unescaped dash is legal following a generic class like \w), but it definitely feels more correct to include the escaping, and adding the escape doesn't break anything. I have adjusted accordingly.

[djones-scu-edu]

I always forget in which RE variations the dash holds no special meaning in a character class if it is the first or last character in the class. In PHP, it appears to be either.

[EreMaijala]

I think that another character we may want to add is underscore.

[demiankatz]

I think that another character we may want to add is underscore.

The \w metacharacter already includes the underscore (it's equivalent to [A-Za-z0-9_]), so I think we're okay here. Not sure why the decision was made to include underscore but not dash!

[EreMaijala]

Okay, good. I forgot that!

[demiankatz]

Okay, good. I forgot that!

Me too; I had to look it up. But it explains why this wasn't caught sooner -- the local_theme_example has always worked and may have set a precedent that others followed instead of using dashes.

[dltj]

Yes! It was the underscores in the “local_theme_example” that had me thinking to try those. Stumbled onto the answer, in other words.