fix: store drag targets in a ref and close #876 (#877)
fix: store drag targets in a ref and close #876 (#877)

This avoids unnecessary renders when drag targets change, which works around an issue where the drag targets get cleared out by the browser when dragging into a child element of the drop zone.
react-dropzone/react-dropzone,react-dropzone/react-dropzone,paramaggarwal/react-dropzone,okonet/react-dropzone,react-dropzone/react-dropzone