VS2013: Adjust libgltf to 12.0 vcproj version

Change-Id: I076c998f5c843b60ac5624381e51271a0924043f
Reviewed-on: https://gerrit.libreoffice.org/10161
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>