link build badge to master branch

and change badges to svg

README.md

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 ## Istanbul - a JS code coverage tool written in JS
 
-[![Build Status](https://secure.travis-ci.org/gotwarlost/istanbul.png)](http://travis-ci.org/gotwarlost/istanbul)
-[![Dependency Status](https://gemnasium.com/gotwarlost/istanbul.png)](https://gemnasium.com/gotwarlost/istanbul)
+[![Build Status](https://secure.travis-ci.org/gotwarlost/istanbul.svg?branch=master)](http://travis-ci.org/gotwarlost/istanbul)
+[![Dependency Status](https://gemnasium.com/gotwarlost/istanbul.svg)](https://gemnasium.com/gotwarlost/istanbul)
 [![Coverage Status](https://img.shields.io/coveralls/gotwarlost/istanbul.svg)](https://coveralls.io/r/gotwarlost/istanbul?branch=master)
 [![bitHound Score](https://www.bithound.io/github/gotwarlost/istanbul/badges/score.svg)](https://www.bithound.io/github/gotwarlost/istanbul)