docs(readme): update badges (#107)

This commit includes the prettier badge and changes the Standard badge
to match the style of the other badges.

Author: macklinu

README.md

@@ -2,9 +2,10 @@
 
 Enforce best practices for JavaScript promises.
 
-[![js-standard-style](https://cdn.rawgit.com/feross/standard/master/badge.svg)](https://github.com/feross/standard)
 [![travis-ci](https://travis-ci.org/xjamundx/eslint-plugin-promise.svg)](https://travis-ci.org/xjamundx/eslint-plugin-promise)
 [![npm version](https://badge.fury.io/js/eslint-plugin-promise.svg)](https://www.npmjs.com/package/eslint-plugin-promise)
+[![JavaScript Style Guide](https://img.shields.io/badge/code_style-standard-brightgreen.svg)](https://standardjs.com)
+[![code style: prettier](https://img.shields.io/badge/code_style-prettier-ff69b4.svg)](https://github.com/prettier/prettier)
 
 <!-- START doctoc generated TOC please keep comment here to allow auto update -->