update README

Author: hunterliu1003

README.md

@@ -71,7 +71,6 @@ These are the features that will be added in the comming weeks:
 
 - draggable modal
 - resizable modal
-- duplicate overlay property
 - dynamic emit modal component with vue directive like:
   - `this.$modal.show('hello-world')`
   - `this.$modal.hide('hello-world')`