fix(scss): should allow multiline comments

[EladBezalel]

Multiline comments:

/**
 * yay
 */

Can't be compiled (in some node versions) with node-sass into 1 line comment,

[devversion]

FYI: Issue is only present in the theming pipeline, since it's not minifying the SCSS.

The most elegant solution would be:

• Minifying the SCSS for the $MD_THEME_CSS constant.
• Not minifying the SCSS, when exporting a release build for bower-material.

[ThomasBurleson]

I think we should minify the $MD_THEME_CSS string.

[devversion]

@ThomasBurleson Agreed. But as said above, we shouldn't minify for bower-material deploys. Pretty simple gulp-if