Add bower and travis badges to README

Author: sharkdp

README.md

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 # purescript-bigints
 
+[![Latest release](http://img.shields.io/bower/v/purescript-bigints.svg)](https://github.com/sharkdp/purescript-bigints/releases)
+[![Build Status](https://api.travis-ci.org/sharkdp/purescript-bigints.svg?branch=master)](https://travis-ci.org/sharkdp/purescript-bigints)
+
 A library for calculations with arbitrary length integers.
 This is a simple wrapper around [BigInteger.js](https://github.com/peterolson/BigInteger.js)
 by [Peter Olson](https://github.com/peterolson).