Updated Renovate configuration (#1137)

no issue
- ignore `ember-exam` until it's compatible with latest stable of `ember-mocha`
  - see https://github.com/ember-cli/ember-exam/issues/238
- moved `ember-exam`, `ember-mocha`, and `testem` into their own group so changes to test env don't cause addon upgrade PRs to fail

ghost/admin/renovate.json

@@ -9,7 +9,8 @@
   "ignoreDeps": [
     "ember-drag-drop",
     "normalize.css",
-    "validator"
+    "validator",
+    "ember-exam"
   ],
   "ignorePaths": ["lib/koenig-editor/package.json"],
   "travis": { "enabled": true },
@@ -25,6 +26,10 @@
       "groupName": "ember core",
       "packageNames": ["ember-source", "ember-cli", "ember-data"]
     },
+    {
+      "groupName": "ember testing",
+      "packageNames": ["ember-mocha", "ember-exam", "testem"]
+    },
     {
       "groupName": "ember addons",
       "packagePatterns": ["^ember", "^@ember", "^broccoli", "^liquid"]