The documentation is now located at docs.typo3.org.
Update the URL accordingly.

Change-Id: Ib9b102e0705742fe0b1498f6a7c22cbc0d23a333
Resolves: #47621
Releases: 6.2, 6.1, 6.0, 4.7, 4.5
Reviewed-on: https://review.typo3.org/20251
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert