[BUGFIX] Typo in Install Tool

Fix a simple typo in mail of Install Tool.

Change-Id: Ibe8b8003cbf6d2b98210bc22bf5e2a5678e0e137
Resolves: #32970
Releases: 4.7, 4.6, 4.5
Reviewed-on: http://review.typo3.org/7671
Reviewed-by: Markus Klein
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert