Fix slight error in snap calculation.
Fix slight error in snap calculation.

Archie22is/stack,SoxFace/stack,mbostock/stack,banj/stack,tailhook/leap_presentation,banj/stack,bondah/GIS_Intro,ee08b397/stack,fbukevin/weic_d3js,ImFreeApp/resource-stack,ee08b397/stack,SoxFace/stack,Archie22is/stack,ImFreeApp/resource-stack,gideonite/WIP,mbostock/stack,atogle/presentations,bondah/GIS_Intro,fbukevin/weic_d3js