meta-gnome: fix typo of directory name

Fix typo of directory name 'recipe-devtools' in meta-gnome. It should
recipes-devtools.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>