[BUGFIX] Fix double slashes in RequireJS config of install tool

RequireJS configs do not have a slash at the end of the path.

The Debug Console shows that files are loaded with double
slashes in the install tool, so they should be avoided.

Resolves: #85481
Releases: master
Change-Id: I80326d176c6dbd54847f1c188d312da1c5e55078
Reviewed-on: https://review.typo3.org/57470


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>