Update arangodb instructions to work with DC/OS 1.11

[judithpatudith]

https://github.com/dcos/examples/tree/master/arangodb

1. Fork the examples repo on GitHub.
2. Make a copy of latest example directory (mostly 1.10 or 1.9) for your package and name it 1.11.
3. On a new branch, test the example on a DC/OS 1.11 cluster. As you test, replace the old screenshots with new ones and make any necessary corrections to the example.
4. Feel free to also improve the instructions.
5. Add a link to your newly created 1.11 example to the README.md file for your package's directory.
6. Report your results: a) If the example works out of the box, or you are able to correct it, open a PR with your changes (including the example itself and its addition to the README.md file) and add it to the issue. b) If you can’t get your example to work, add a detailed description of what went wrong on the issue (you still get stickers!).

When you’re done, email [email protected] with the following information: Subject: 1.11 Example Testing - [Service Name] Body:

• Your name
• GitHub Issue link
• Your Twitter handle, if you have one
• Community Slack handle, if you have one
• Mailing address (for the stickers)