Correct --sign-off to --signoff in bot feedback

[rgee0]

Signed-off-by: Richard Gee richard@technologee.co.uk

Description

Amends references to --sign-off with --signoff as per git client help.

       -s, --signoff
           Add Signed-off-by line by the committer at the end of the commit log message. The meaning of a signoff depends
           on the project, but it typically certifies that committer has the rights to submit this work under the same
           license and agrees to a Developer Certificate of Origin (see http://developercertificate.org/ for more
           information).

Motivation and Context

The message was wrong. It's now correct. Also updated the GET.md reference.

How Has This Been Tested?

Trivial non-invasive change

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I've read the CONTRIBUTION guide
• [x] I have signed-off my commits with git commit -s
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[rgee0]

Reference openfaas/docs#151

[alexellis]

Thank you for getting this turned around so quickly.