Fix reading of cookies

In Gerrit versions newer than 3.4, the utils-class was not accessible
anymore by plugins and thus using it to find a cookie didn't work anymore.

Change-Id: I9b923dc769adb5a819d7bde7d2d977733b800e06

gr-messageoftheday/gr-messageoftheday-banner.js

diff --git a/gr-messageoftheday/gr-messageoftheday-banner.js b/gr-messageoftheday/gr-messageoftheday-banner.js
index ae84e85..1a351a9 100644
--- a/gr-messageoftheday/gr-messageoftheday-banner.js
+++ b/gr-messageoftheday/gr-messageoftheday-banner.js
@@ -57,7 +57,7 @@
   }
 
   _isHidden() {
-    this._hidden = window.util.getCookie(`msg-${this._message.id}`) === '1';
+    this._hidden = document.cookie.search(`msg-${this._message.id}=`) > -1;
   }
 }