added "font-kerning" in the font key

lib/single-file/css-fonts-minifier.js

@@ -298,6 +298,7 @@ this.fontsMinifier = this.fontsMinifier || (() => {
 		return JSON.stringify([
 			getFontFamilyName(style.getPropertyValue("font-family")),
 			getFontWeight(style.getPropertyValue("font-weight")),
+			style.getPropertyValue("font-kerning"),
 			style.getPropertyValue("font-style"),
 			style.getPropertyValue("unicode-range"),
 			getFontStretch(style.getPropertyValue("font-stretch")),