chore: Update README.md (hiddentao#293)

Update badge urls and extensions.

README.md

@@ -1,10 +1,10 @@
 # squel - SQL query string builder
 
-[![Build Status](https://secure.travis-ci.org/hiddentao/squel.png?branch=master)](http://travis-ci.org/hiddentao/squel)
+[![Build Status](https://secure.travis-ci.org/hiddentao/squel.svg?branch=master)](http://travis-ci.org/hiddentao/squel)
 [![CDNJS](https://img.shields.io/cdnjs/v/squel.svg)](https://cdnjs.com/libraries/squel)
-[![NPM module](https://badge.fury.io/js/squel.png)](https://badge.fury.io/js/squel)
+[![NPM module](https://badge.fury.io/js/squel.svg)](https://badge.fury.io/js/squel)
 [![NPM downloads](https://img.shields.io/npm/dm/squel.svg?maxAge=2592000)](https://www.npmjs.com/package/squel)
-[![Join the chat at https://discord.gg/PBAR2Bz](https://img.shields.io/badge/discord-join%20chat-738bd7.svg?style=flat-square)](https://discord.gg/PBAR2Bz)
+[![Join the chat at https://discord.gg/PBAR2Bz](https://img.shields.io/badge/discord-join%20chat-738bd7.svg)](https://discord.gg/PBAR2Bz)
 [![Follow on Twitter](https://img.shields.io/twitter/url/http/shields.io.svg?style=social&label=Follow&maxAge=2592000)](https://twitter.com/hiddentao)
 
 A flexible and powerful SQL query string builder for Javascript.