add app-compat to devDeps

Author: Feiyang1

packages/database-compat/package.json

@@ -33,5 +33,8 @@
     "@firebase/util": "1.3.0",
     "@firebase/component": "0.5.6",
     "tslib": "^2.1.0"
+  },
+  "devDependencies": {
+    "@firebase/app-compat": "0.1.1"
   }
 }