tns package-manager set invalid_value does not say pnpm is supported

[rosen-vladimirov]

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: 6.4.0
• Cross-platform modules: Not applicable
• Android Runtime: Not applicable
• iOS Runtime: Not applicable
• Plugin(s): Not applicable

Describe the bug
When calling tns package-manager set with invalid value, the command says only npm and yarn are supported, while in fact pnpm is also supported.

To Reproduce

tns package-manager set invalid_value
invalid_value is not a valid package manager. Only yarn or npm are supported.

Expected behavior
The error message should list all supported options.

Sample project

Additional context