fix: lerna dependencies are also in the create-app part

package.json

@@ -50,7 +50,7 @@
     "concurrently": "^5.2.0",
     "fs-extra": "^9.0.0",
     "husky": "^4.2.3",
-    "lerna": "^3.20.2",
+    "lerna": "^4.0.0",
     "lint-staged": "^10.1.0",
     "prettier": "^2.0.5",
     "recursive-readdir": "^2.2.2",

packages/create-app/templates/default-app/package.json.hbs

@@ -30,7 +30,7 @@
   "devDependencies": {
     "@backstage/cli": "^{{version '@backstage/cli'}}",
     "@spotify/prettier-config": "^7.0.0",
-    "lerna": "^3.20.2",
+    "lerna": "^4.0.0",
     "prettier": "^1.19.1"
   },
   "prettier": "@spotify/prettier-config",