Move hostname to last argument on mac

[dopecodez]

As per PR #12 , we moved the hostname to the last argument on the ping command on linux.

I propose we do the same for Mac so as to maintain uniformity between the UNIX platforms.

All we need to do is follow the steps as in #12.

• Move hostname to last argument in src/builder/mac.ts
• Adjust the tests in test/builder/builder.ts

I'll take this up once i get the time. Anyone who wants to work on this on the meantime, can comment here if you want a more detailed idea about what we're trying to achieve.