(mac-os) is_supported func can be optimised.

[anubhavitis]

What current implementation is trying to do is:

• get the os_version in vec format
• convert it into String
• convert it into f64
• then compare

What we can simply do is:

• get the os_version in vec format
• convert the min_version into vec format
• then compare

[anubhavitis]

Check this PR https://github.com/clearlysid/cypher/pull/13