fixed script execution issue

lib/single-file/css-minifier.js

@@ -20,7 +20,7 @@
 
 /* global CSSRule, cssWhat, parseCss, RulesMatcher */
 
-this.cssMinifier = this.stylesMinifier || (() => {
+this.cssMinifier = this.cssMinifier || (() => {
 
 	const SEPARATOR_TYPES = ["descendant", "child", "sibling", "adjacent"];
 	const REMOVED_PSEUDO_CLASSES = ["focus", "focus-within", "hover", "link", "visited", "active"];