Modernize ES for-loops and remove problematic for-in loops

This slightly modifies the behaviour of errors (see init.js)

Change-Id: I1aab691d5b7e8167b6213378bdd9139c133202cd
diff --git a/dev/js/src/panel/result.js b/dev/js/src/panel/result.js
index d221081..3c5dc31 100644
--- a/dev/js/src/panel/result.js
+++ b/dev/js/src/panel/result.js
@@ -30,9 +30,7 @@
         var resultButtons = KorAP.Plugin.buttonGroup("result");
 
         // Add all result buttons in order
-        for (i in resultButtons) {
-          this.actions.add.apply(this.actions, resultButtons[i]);
-        };
+       resultButtons.forEach(i => this.actions.add.apply(this.actions, i));
 
         KorAP.Plugin.clearButtonGroup("result");
       };