yaml-cpp: tie recipe to git revision instead of dynamicly generated tarball
yaml-cpp: tie recipe to git revision instead of dynamicly generated tarball

Since Github's auto-generated tarballs aren't garanteed to be identical
over time it's better to tie the recipe to a git revision.

closes #552

Signed-off-by: Dmitry Rozhkov <208d90a35521dcb3e50d907c695d85f9e609147c@linux.intel.com>

bulwahn/meta-ros,bmwcarit/meta-ros,bulwahn/meta-ros,bmwcarit/meta-ros,bmwcarit/meta-ros,bulwahn/meta-ros,bmwcarit/meta-ros