ui dependencies: specify @ember

out of an abundance of caution, we should avoid having the package manager making inferrences.

ui/lib/core/package.json

@@ -18,7 +18,7 @@
     "ember-cli-typescript": "*",
     "ember-composable-helpers": "*",
     "ember-concurrency": "*",
-    "ember/render-modifiers": "*",
+    "@ember/render-modifiers": "*",
     "ember-power-select": "*",
     "ember-router-helpers": "*",
     "ember-svg-jar": "*",