Specify a peer on ember-source

Author: NullVoxPopuli

addon/package.json

@@ -47,6 +47,9 @@
     "start": "rollup --config --watch --no-watch.clearScreen",
     "test": "echo 'A v2 addon does not have tests, run tests in test-app'"
   },
+  "peerDependencies": {
+    "ember-source": ">= 4.0.0"
+  },
   "dependencies": {
     "@ember/test-waiters": "^3.1.0",
     "@embroider/addon-shim": "^1.8.7",