[TASK] Fix travis builds

Due some regressions on side of travis
(https://github.com/travis-ci/travis-ci/issues/1710) an older git version
is used which doesn't support things like "--single-branch".

To avoid this, git is updated to latest version on the build server before
starting cloning

Change-Id: Ic5f698e84f378b9fed6bd64398b8058a20be860e
Resolves: #54369
Releases: 6.2
Reviewed-on: https://review.typo3.org/26366
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer