[TASK] Fix composer branch alias for 6.2 branch

The composer.json file wrongly configures the
master branch to be aliased to 6.2.x-dev

Fix it by aliasing our TYPO3_6-2 branch to 6.2.x-dev

Releases: 6.2
Change-Id: I89d91aa011cc384e0868913bbbe3add50585866e
Reviewed-on: https://review.typo3.org/31605
Reviewed-by: Christian Opitz <christian.opitz@netresearch.de>
Tested-by: Christian Opitz <christian.opitz@netresearch.de>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>