fixes triangle winding direction for ofIcoSphere

triangles were wound the other way around, which resulted in backfaces to be rendered instead of front faces when glEnable(GL_CULL_FACE), glCullFace(GL_BACK) was applied.

This reverses the triangle winding mode - and so fixes it.

fixes #2263

![screen shot 2013-07-16 at 12 45 09](https://f.cloud.github.com/assets/423509/804413/31832956-ee0d-11e2-8d1d-7fa91fba0b4a.png)

(icosphere on the left, note that @nickhardeman's PR #2259 fixes the cone not being rendered correctly, too. =)

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>