[Request] Add share.js

[mdluo]

Library name: share.js
Git repository url: https://github.com/overtrue/share.js
npm package url(optional): https://www.npmjs.com/package/social-share.js
License(s): MIT
Official homepage: http://overtrue.me/share.js/
Wanna say something? Leave message here:
share.js is a library to create social share buttons, including Facebook, Twitter, Linkedin, Google+ and the most popular social media in China: Weibo, Qzone, QQ, Wechat, Douban, Diandian and more.

Notes from cdnjs maintainer:
You are welcome to add a library via sending pull request,
it'll be faster then just opening a request issue,
and please don't forget to read the guidelines for contributing, thanks!!