Update README.md

Fixed a buggy URL link to the Coverage badge status to Coveralls

Author: PyDataBlog

README.md

@@ -3,4 +3,4 @@
 [![Stable](https://img.shields.io/badge/docs-stable-blue.svg)](https://PyDataBlog.github.io/ParallelKMeans.jl/stable)
 [![Dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://PyDataBlog.github.io/ParallelKMeans.jl/dev)
 [![Build Status](https://www.travis-ci.org/PyDataBlog/ParallelKMeans.jl.svg?branch=master)](https://www.travis-ci.org/PyDataBlog/ParallelKMeans.jl)
-[![Coveralls](https://coveralls.io/repos/github/PyDataBlog/ParallelKMeans.jl/badge.svg?branch=master)](https://coveralls.io/github/PyDataBlog/ParallelKMeans.jl?branch=master)
+[![Coverage Status](https://coveralls.io/repos/github/PyDataBlog/ParallelKMeans.jl/badge.svg?branch=master)](https://coveralls.io/github/PyDataBlog/ParallelKMeans.jl?branch=master)