Use get instead of fetchJSON for getting checkers

Change-Id: Id292ba0574c569478288e8a2273754774d0c07c0
diff --git a/gr-checks/gr-checkers-list.js b/gr-checks/gr-checkers-list.js
index d2c7256..4914274 100644
--- a/gr-checks/gr-checkers-list.js
+++ b/gr-checks/gr-checkers-list.js
@@ -123,10 +123,7 @@
 
     _getCheckers(pluginRestApi) {
       if (!pluginRestApi) return;
-      pluginRestApi.fetchJSON({
-        method: 'GET',
-        url: GET_CHECKERS_URL,
-      }).then(checkers => {
+      pluginRestApi.get(GET_CHECKERS_URL).then(checkers => {
         if (!checkers) { return; }
         this._checkers = checkers;
         this._startingIndex = 0;