Fix default mapping of the Voronoi texture

I'm loving the improvements the shader nodes are getting, and especially with voronoi. However, to use the voronoi properly for some applications such as creating "pixelated" mapping, I have to fix the mapping every time I use it because it's always half a square off. I propose to add this fix by default. It's pretty dang simple to fix, however I don't know how to patch it myself because I'm not familiar with coding