[BUGFIX] Fix installer symlink generation on Windows

Resolves: #70262
Releases: master
Related: https://github.com/TYPO3/CmsComposerInstallers/pull/22
Change-Id: I8582b3dd901cbd3aaede0509136d7f6dbc723b87
Reviewed-on: http://review.typo3.org/43908


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Tested-by: Helmut Hummel <helmut.hummel@typo3.org>