Update 12-context.md

[inkinworld]

Before submitting a pull request, please make sure the following is done...

1. Fork the repo and create your branch from master.
2. If you've added code that should be tested, add tests!
3. If you've changed APIs, update the documentation.
4. Ensure the test suite passes (grunt test).
5. Make sure your code lints (grunt lint) - we've done our best to make sure these rules match our internal linting guidelines.
6. If you haven't already, complete the CLA.

Modify a clerical error

[ghost]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file. In order for us to review and merge your code, please sign up at https://code.facebook.com/cla - and if you have received this in error or have any questions, please drop us a line at cla@fb.com. Thanks!

[inkinworld]

I have sign up at cla

[ghost]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[jimfb]

Thanks!