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

首先复现 issue 中的两个命令：tns run ios --bundle，然后是 tns run ios --bundle --env.uglify，并比较构建日志。阅读 NativeScript CLI 的构建和打包入口点，以确定更改 --env.uglify 是否应该使现有构建失效；当行为和预期结果已记录在文档中，并由回归测试覆盖时，即视为完成。