change to use hackage badge provided by shields.io

README.md

@@ -1,6 +1,6 @@
 sign
 ====
 
-[![Build Status](https://secure.travis-ci.org/msakai/sign.png?branch=master)](http://travis-ci.org/msakai/sign) [![Build status](https://ci.appveyor.com/api/projects/status/txxfj27tg5ee6ma2/branch/master?svg=true)](https://ci.appveyor.com/project/msakai/sign/branch/master) [![Hackage](https://budueba.com/hackage/sign)](https://hackage.haskell.org/package/sign) [![Coverage Status](https://coveralls.io/repos/msakai/sign/badge.svg)](https://coveralls.io/r/msakai/sign)
+[![Build Status](https://secure.travis-ci.org/msakai/sign.png?branch=master)](http://travis-ci.org/msakai/sign) [![Build status](https://ci.appveyor.com/api/projects/status/txxfj27tg5ee6ma2/branch/master?svg=true)](https://ci.appveyor.com/project/msakai/sign/branch/master) [![Hackage](https://img.shields.io/hackage/v/sign.svg)](https://hackage.haskell.org/package/sign) [![Coverage Status](https://coveralls.io/repos/msakai/sign/badge.svg)](https://coveralls.io/r/msakai/sign)
 
 Arithmetic over signs (i.e. {-,0,+}) and sets of signs