Error when version field is not present in the libman.json file does not indicate that version is a required field.

[prafullbhosale]

Minimal repro steps

1. Delete the "version": "1.0" field from a libman.json file.
2. Restore client side libraries

Expected result

The error informs that the version field is required.

Actual result

The error message is: Version "" is not supported by this version of Library Manager

/cc @justcla