avoid the presence of .html twice in the file name

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

@@ -257,7 +257,7 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 				title = titleElement.textContent.trim();
 			}
 			return {
-				title: title || (this.baseURI ? this.baseURI.match(/([^/]*)\/?$/)[1] : ""),
+				title: title || (this.baseURI ? this.baseURI.match(/([^/]*)\/?(\.html?.*)$/)[1] : ""),
 				content: this.dom.serialize()
 			};
 		}