fixed typo

lib/single-file/util/doc-util-core.js

@@ -46,7 +46,7 @@ this.DocUtilCore = this.DocUtilCore || (() => {
 				};
 			}
 
-			return class DocUtl {
+			return class DocUtil {
 				static async getContent(resourceURL, options) {
 					return domUtil.getContent(resourceURL, options);
 				}