Drop macOS Sierra support

[Natalia-Hristova]

Please, provide the details below:

Did you verify this is a real problem by searching the NativeScript Forum and the other open issues in this repo?

Tell us about the problem

In v. 5.0.0 ios runtime is dropping iOS Inspector support for Sierra because of very low usage with this macOS. Still users can debug with iOS Inspector on macOS >= 10.13 or use default inspector - Chrome DevTools

1. Currently CLI prints warning for Sierra deprecation that should be updated:

Support for macOS 10.12 is deprecated and will be removed in one of the next releases of NativeScript. Please, upgrade to the latest macOS version.

2. Also when command tns debug ios --inspector is run, CLI has to check macOS version and in case it is < 10.13 to inform the user and stops the command execution.

3. In docs macOS Requirements have to be updated as well

https://docs.nativescript.org/start/general-requirements#macos-requirements

Which platform(s) does your issue occur on?

iOS/Android/Both

Please provide the following version numbers that your issue occurs with:

• CLI: 4.2.3

Please tell us how to recreate the issue in as much detail as possible.

Try to execute CLI command on macOS Sierra

Is there code involved? If so, please share the minimal amount of code needed to recreate the problem.

Consider using the playground to provide the code you have issues with.