README: Use SVG badges (#507)

* README: Use SVG badges

* switch travis-ci endpoint to live domain

Co-authored-by: Florent Monbillard <f.monbillard@gmail.com>
Co-authored-by: Thomas McDonald <thomasm@palantir.com>

README.md

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-# rolify [![Gem Version](https://badge.fury.io/rb/rolify.svg)](http://badge.fury.io/rb/rolify) [![build status](https://secure.travis-ci.org/RolifyCommunity/rolify.png)](http://travis-ci.org/RolifyCommunity/rolify) [![Code Climate](https://codeclimate.com/github/RolifyCommunity/rolify.png)](https://codeclimate.com/github/RolifyCommunity/rolify) [![Coverage Status](https://coveralls.io/repos/RolifyCommunity/rolify/badge.svg?branch=master&service=github)](https://coveralls.io/github/RolifyCommunity/rolify?branch=master)
+# rolify [![Gem Version](https://badge.fury.io/rb/rolify.svg)](http://badge.fury.io/rb/rolify) [![build status](https://travis-ci.org/RolifyCommunity/rolify.svg)](http://travis-ci.org/RolifyCommunity/rolify) [![Code Climate](https://codeclimate.com/github/RolifyCommunity/rolify.svg)](https://codeclimate.com/github/RolifyCommunity/rolify) [![Coverage Status](https://coveralls.io/repos/RolifyCommunity/rolify/badge.svg?branch=master&service=github)](https://coveralls.io/github/RolifyCommunity/rolify?branch=master)
 
 Very simple Roles library without any authorization enforcement supporting scope on resource object.