Enhancement - Check for update on launch

[DeezyE]

Updated ./beef launch script to check if the origin/master branch is on a different commit, if so will prompt for the update.
This should make the update prompt less frequent and speed up beef launch.

Also addressed some minor rubocop complaints

[wheatley]

@DeezyE as discussed there might be an issue with this and Kali.
We should check if this is a git repo or if it is the Kali distro before checking the update.

What did you think?

[DeezyE]

@wheatley thanks I'll make that change

[DeezyE]

I've added some logic to only check for update if '.git' is present to account for Kali package installation. Also cleaned up some redundant variables that I had made previously