Fixed a bug that was distributed betwwen conrod and opengl_graphics
See PistonDevelopers/conrod#1274
Turns out that a fix in piston2d-opengl_graphics was necessary to fix this:
PistonDevelopers/opengl_graphics#303
Use version 0.60 of piston2d-opengl_graphics and version 0.65 of conrod to fix the problem.