message: set top, zIndex default props on Sticky
diff: @@ -17,3 +17,7 @@ export const Absolute = withPosition('absolute')
  export const Fixed = withPosition('fixed')
  export const Relative = withPosition('relative')
  export const Sticky = withPosition('sticky')
  +Object.assign(Sticky.defaultProps, {
  + top: 0,
  + zIndex: 1
  +})
  