Docs: Fixed README.md (#3612)

* Docs: Fixed README.md

* Docs: fixed README.md

README.md

 <p align="center">
   <img src="https://cdn.rawgit.com/ElemeFE/element/dev/element_logo.svg">
 </p>
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 # Element
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 [![Build Status](https://travis-ci.org/ElemeFE/element.svg?branch=master)](https://travis-ci.org/ElemeFE/element)
 [![Coverage Status](https://coveralls.io/repos/github/ElemeFE/element/badge.svg?branch=master)](https://coveralls.io/github/ElemeFE/element?branch=master)
 [![CDNJS](https://img.shields.io/cdnjs/v/element-ui.svg)](https://cdnjs.com/libraries/element-ui)