fix: dummy app needed ember-cli-string-helpers

Author: tzellman

package-lock.json

@@ -54,6 +54,7 @@
     "ember-cli-inject-live-reload": "^2.0.2",
     "ember-cli-postcss": "^7.0.0",
     "ember-cli-sri": "^2.1.1",
+    "ember-cli-string-helpers": "^5.0.0",
     "ember-cli-terser": "^4.0.1",
     "ember-disable-prototype-extensions": "^1.1.3",
     "ember-export-application-global": "^2.0.1",