`-o` and `--os` is not compliant with the client spec

[marchersimon]

According to the client spec, the arguments for platform-specific commands should be -p and --platform. However, here it is -o and --os.

Reference: tldr-pages/tldr#5508 (comment)

[vladimyr]

Well as it is the case with any good spec implementation here simply precedes it 😀