Fix coveralls badge (use branch name as SVG name)

README.md

@@ -1,4 +1,4 @@
-![](https://raw.github.com/wiki/brettwooldridge/HikariCP/Hikari.png) HikariCP <sup><sup>It's Faster.&nbsp;</sup></sup>[![Travis branch](https://img.shields.io/travis/joyent/node/v0.6.svg)](https://travis-ci.org/brettwooldridge/HikariCP)<img src='https://raw.github.com/wiki/brettwooldridge/HikariCP/space60x1.gif' width='3px'>[![Issue Stats](http://issuestats.com/github/brettwooldridge/HikariCP/badge/issue)](http://issuestats.com/github/brettwooldridge/HikariCP)<img src='https://raw.github.com/wiki/brettwooldridge/HikariCP/space60x1.gif' width='3px'>[![Coverage Status](https://img.shields.io/coveralls/brettwooldridge/HikariCP.svg)](https://coveralls.io/r/brettwooldridge/HikariCP?branch=2.3.0)<br><sub><sub><sup>Hi·ka·ri [hi·ka·'lē] &#40;*Origin: Japanese*): light; ray.</sup></sub></sub>
+![](https://raw.github.com/wiki/brettwooldridge/HikariCP/Hikari.png) HikariCP <sup><sup>It's Faster.&nbsp;</sup></sup>[![Travis branch](https://img.shields.io/travis/joyent/node/v0.6.svg)](https://travis-ci.org/brettwooldridge/HikariCP)<img src='https://raw.github.com/wiki/brettwooldridge/HikariCP/space60x1.gif' width='3px'>[![Issue Stats](http://issuestats.com/github/brettwooldridge/HikariCP/badge/issue)](http://issuestats.com/github/brettwooldridge/HikariCP)<img src='https://raw.github.com/wiki/brettwooldridge/HikariCP/space60x1.gif' width='3px'>[![Coverage Status](https://img.shields.io/coveralls/brettwooldridge/HikariCP/2.3.0.svg)](https://coveralls.io/r/brettwooldridge/HikariCP?branch=2.3.0)<br><sub><sub><sup>Hi·ka·ri [hi·ka·'lē] &#40;*Origin: Japanese*): light; ray.</sup></sub></sub>
 ==========
 
 Fast, simple, reliable.  HikariCP is a "zero-overhead" production ready JDBC connection pool.  Coming in at roughly 70Kb, the library is very light.  Read about [how we do it here](https://github.com/brettwooldridge/HikariCP/wiki/Down-the-Rabbit-Hole).