Move 'use strict' to file level

Change-Id: I1f0dae4aa168e77c112bcd3688c98b84e4ce5f36
diff --git a/dev/js/src/util.js b/dev/js/src/util.js
index 8e40c12..0fea33f 100644
--- a/dev/js/src/util.js
+++ b/dev/js/src/util.js
@@ -1,3 +1,5 @@
+"use strict";
+
 window.KorAP = window.KorAP || {};
 
 // Don't let events bubble up