cube-gears: Change header file to <GLES3/gl3.h>
Since commit 96d63eb5 (" kmscube: Add gears mode"), kmscube fails to build on platforms without <GL/gl.h>.
Fix it by changing the header file to <GLES3/gl3.h>.
Reported-by: Martin Jansa martin.jansa@gmail.com Suggested-by: Martin Jansa martin.jansa@gmail.com Signed-off-by: Fabio Estevam festevam@gmail.com