message: fix conflict between ember-let and ember-let-polyfill
  And re-add jquery.
diff: "@cardstack/rendering": "0.14.0",
  "@cardstack/test-support": "0.14.0",
  "@cardstack/tools": "0.14.0",
  + "@ember/jquery": "^0.6.0",
  "broccoli-asset-rev": "^2.4.5",
  "ember-cli": "^3.0.0",
  "ember-cli-dependency-checker": "^2.1.0",
  "ember-data": "^3.5.0",
  "ember-disable-prototype-extensions": "^1.1.2",
  "ember-export-application-global": "^2.0.0",
  - "ember-let": "^0.7.1",
  + "ember-let-polyfill": "^0.1.0",
  "ember-load-initializers": "^1.0.0",
  "ember-maybe-import-regenerator": "^0.1.6",
  "ember-resolver": "^4.0.0",
  