Upgrade dc to 1.6.0

From: https://github.com/NickQiZhu/dc.js/releases/tag/1.6.0

https://github.com/NickQiZhu/dc.js/raw/1.6.0/dc.css
https://github.com/NickQiZhu/dc.js/raw/1.6.0/dc.js
https://github.com/NickQiZhu/dc.js/raw/1.6.0/dc.min.js
https://github.com/NickQiZhu/dc.js/raw/1.6.0/dc.min.js.map
https://github.com/NickQiZhu/dc.js/raw/1.6.0/package.json