[TASK] Added .sass-cache to .gitignore

Releases: 6.2
Change-Id: I3278984b1a7aa4ee704b9568f01d3ff3edf94da9
Reviewed-on: https://review.typo3.org/28617
Reviewed-by: Wouter Wolters
Reviewed-by: Ernesto Baschny
Tested-by: Ernesto Baschny