travis-ci: run tests against default Git and latest Git
travis-ci: run tests against default Git and latest Git

Run Git-LFS tests against the Travis-CI default Git version and the
latest available Git version on the respective platform.

The default Git version is currently 1.8.5.6 on Ubuntu and 1.9.3 on OSX.

bozaro/git-lfs,andyneff/git-lfs,andyneff/git-lfs,aleb/git-lfs,Jericho25/-git-lfs_miilkyway,dakotahawkins/git-lfs,aleb/git-lfs,Jericho25/-git-lfs_miilkyway,bozaro/git-lfs,github/git-lfs,ttaylorr/git-lfs,bozaro/git-lfs,larsxschneider/git-lfs,ttaylorr/git-lfs,andyneff/git-lfs,ttaylorr/git-lfs,larsxschneider/git-lfs,larsxschneider/git-lfs,dakotahawkins/git-lfs,Jericho25/-git-lfs_miilkyway,github/git-lfs,dakotahawkins/git-lfs,github/git-lfs,aleb/git-lfs