Removed the forkMe ribbon for mobile devices

[Anshul-target]

Make sure these boxes are checked before your pull request (PR) is ready to be reviewed and merged. Thanks!

• [ ] tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR -- or run tests locally with rake test
• [ ] code is in uniquely-named feature branch and has no merge conflicts
• [ ] PR is descriptively titled
• [ ] PR body includes fixes #0000-style reference to original issue #
• [ ] ask @publiclab/reviewers for help, in a comment below

We're happy to help you get this ready -- don't be afraid to ask for help, and don't be discouraged if your tests fail at first!

If tests do fail, click on the red X to learn why by reading the logs.

Please be sure you've reviewed our contribution guidelines at https://publiclab.org/contributing-to-public-lab-software

We have a loose schedule of reviewing and pulling in changes every Tuesday and Friday, and publishing changes on Fridays.

Thanks!

[Anshul-target]

@publiclab/reviewers please review