Move 'use strict' to file level

Change-Id: I1f0dae4aa168e77c112bcd3688c98b84e4ce5f36
diff --git a/dev/js/src/loc/de.js b/dev/js/src/loc/de.js
index d42af7f..21bf629 100644
--- a/dev/js/src/loc/de.js
+++ b/dev/js/src/loc/de.js
@@ -1,3 +1,5 @@
+"use strict";
+
 define(function () {
   const loc = KorAP.Locale;
   loc.OR = 'oder';