Use array spread again

Now that Node.js v4 is explicitly not supported, we can make use of
this feature again.

This reverts commit 634622d.

src/cli-flags-helper.js

@@ -32,7 +32,7 @@ module.exports = {
     } else if (typeof ONLY != "undefined" && targetList.has(ONLY)) {
       return [ONLY];
     } else {
-      return Array.from(targetList);
+      return [...targetList];
     }
   },
   targetList: targetList