Fix failing to install due to app yarn install

Actually not sure this will work, but let's try.
If that works, that means we're back to pre-
nativefier#898 (comment) ,
with a 60s timeout due to npm bug npm/cli#757

Looking at a real fix, potentially coming back to `webpack` the app.

package.json

@@ -39,7 +39,7 @@
     "lint:format": "prettier --write 'src/**/*.js' 'app/src/**/*.js'",
     "lint": "eslint . --ext .ts",
     "list-outdated-deps": "npm out; cd app && npm out; true",
-    "postinstall": "cd app && yarn install --no-lockfile --no-progress --silent",
+    "postinstall": "cd app && echo '***** Installation will take 60s to finish, this is a bug ( https://github.com/jiahaog/nativefier/issues/923 ) that will be addressed in a future release. For now, have a cup of tea. *****' && npm install --no-package-lock --no-audit --silent",
     "test:integration": "jest --testRegex '.*integration-test.js'",
     "test:manual": "npm run build && ./docs/manual-test",
     "test:unit": "jest",
@@ -69,8 +69,7 @@
     "sanitize-filename": "1.x",
     "shelljs": "0.x",
     "source-map-support": "0.x",
-    "tmp": "0.x",
-    "yarn": "1.x"
+    "tmp": "0.x"
   },
   "devDependencies": {
     "@types/jest": "25.x",