Update CLA link in Contributing docs

[calvinf]

Replacing old URL redirect with the new JS Foundation URL

What is the purpose of this pull request? (put an "X" next to item)

[X] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

Update a URL in the Markdown contributing doc.

Is there anything you'd like reviewers to focus on?

The URL.

[jsf-clabot]

All committers have signed the CLA.

[eslintbot]

Thanks for the pull request, @calvinf! I took a look to make sure it's ready for merging and found some changes are needed:

• The commit summary needs to begin with a tag (such as Fix: or Update:). Please check out our guide for how to properly format your commit summary and update it on this pull request.

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[not-an-aardvark]

Thanks for the PR! This looks good to me.

Now that the URL for the CLA is correct, would you mind signing it so that we can merge your PR?

[calvinf]

I've signed the CLA.