[TASK] Update copyright year in documentation to 2018

Resolves: #83453
Releases: master, 8.7, 7.6
Change-Id: I40654f5c230e0e91b3b479dd1c07eb087e639051
Reviewed-on: https://review.typo3.org/55247


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>