Add Webpack 4 support

[sentience]

We aren’t aware of any specific compatibility issues with this loader and Webpack 4, but we haven’t yet tested it extensively, and so the current release still specifies webpack <4 in its peerDependencies.

We’d appreciate hearing from anyone who’s tried this loader with Webpack 4 and is able to report on how/if it worked for them. If not, we will eventually update this ourselves when we upgrade to Webpack 4.

[michaeljones]

Just trying to update to webpack 4 now and found that this line wasn't caught:

var _user$project$Zap_View_Link_Button$cssm = A2(
	_cultureamp$elm_css_modules_loader$CssModules$css,
	'./Zap/View/Button.cssm.scss',
	{btn: '', large: '', primary: '', secondary: '', $default: '', danger: '', safety: '', submit: ''});

I suspect it is due to how the default name is escaped. Perhaps it was handled differently in previous versions. The currently used regex for the JS object doesn't allow for $.

If I change this to include a $ then it seems to work.