Add documentation to $interval.cancel();

[SAFAD]

I have been looking around and was not able to find any informations on how to clear the $interval but reading the source code, sharing is caring!

[mary-poppins]

Thanks for the PR! Please check the items below to help us merge this faster. See the contributing docs for more information.

• Uses the issue template (#6367)

If you need to make changes to your pull request, you can update the commit with git commit --amend.
Then, update the pull request with git push -f.

Thanks again for your help!

[caitp]

There is method documentation for the cancel method, although it might be a bit lacking in depth.

edit I guess this is for ngMocks, hmm lemmec... I guess this is okay, alright.

[caitp]

Merged, thanks