make sure setAttribute is called with 2 params (fix #808)

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

@@ -1065,7 +1065,7 @@ class Processor {
 						const templateElement = doc.createElement("template");
 						templateElement.setAttribute(SHADOW_MODE_ATTRIBUTE_NAME, shadowRootData.mode);
 						if (shadowRootData.delegatesFocus) {
-							templateElement.setAttribute(SHADOW_DELEGATE_FOCUS_ATTRIBUTE_NAME);
+							templateElement.setAttribute(SHADOW_DELEGATE_FOCUS_ATTRIBUTE_NAME, "");
 						}
 						if (shadowRootData.adoptedStyleSheets) {
 							shadowRootData.adoptedStyleSheets.forEach(stylesheetContent => {