Example simulation.jl works on OS X

[mschauer]

Just a heads up that

https://github.com/JuliaGL/GLVisualize.jl/blob/master/examples/introduction/simulation.jl

on OS X apparently does not "generates cool smoke like artifacts". So if it is desired, the video on the home page can be generated without those artifacts. Close issue at discretion.