`tns package-manager set <valid value>` does not give any output

[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
The tns package-manager set <valid value> command does not give any information if the operation succeeds.

To Reproduce
tns package-manager set npm - nothing is printed.

Expected behavior
Show some information that the package-manager is set.