Application is rebuilt when passing --env.uglify for a first time

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 5.2.0
• Android Runtime: 5.2.0
• iOS Runtime: 5.2.0

Describe the bug
when you run project with: tns run ios --bundle and then with: tns run ios --bundle --env.uglify, you will see that the project will pass through building process.

To Reproduce

1. tns create appNG --ng
2. tns run ios --bundle
3. stop the process
4. tns run ios --bundle --env.uglify
   you will see : Building project..., Project successfully built. in console logs

Expected behavior
not sure this behavior is correct

Commencez par reproduire les deux commandes de l’issue : tns run ios --bundle, suivie de tns run ios --bundle --env.uglify, puis comparez les logs du build. Lisez les points d’entrée de build et de bundling de NativeScript CLI afin de déterminer si la modification de --env.uglify devrait invalider le build existant ; le travail est terminé lorsque le comportement et le résultat attendu sont documentés et couverts par un test de régression.