add .onion

[jschauma]

Add .onion as a TLD, for use with, for example, https://facebookcorewwwi.onion/.

[caniszczyk]

Would like to see this cc: @jakl and @bigloser :)

[bigloser]

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}