Add app-exp to devDependencies

Author: sam-gc

packages-exp/auth-exp/package.json

@@ -37,6 +37,7 @@
   "license": "Apache-2.0",
   "devDependencies": {
     "@rollup/plugin-strip": "^1.3.2",
+    "@firebase/app-exp": "0.x",
     "rollup": "1.32.1",
     "rollup-plugin-json": "4.0.0",
     "rollup-plugin-replace": "2.2.0",