Readme: Update badges

Avoid caching the version badge for 30 days.

Ref https://github.com/badges/shields/blob/3.2.0/core/base-service/base.js#L146-L150

Author: Krinkle

README.md

@@ -1,8 +1,8 @@
 # js-reporters
 
 [![Build Status](https://travis-ci.org/js-reporters/js-reporters.svg?branch=master)](https://travis-ci.org/js-reporters/js-reporters)
-[![npm](https://img.shields.io/npm/dm/js-reporters.svg?maxAge=2592000)](https://www.npmjs.com/package/js-reporters)
-[![npm](https://img.shields.io/npm/v/js-reporters.svg?maxAge=2592000)](https://www.npmjs.com/package/js-reporters)
+[![npm](https://img.shields.io/npm/dm/js-reporters.svg)](https://www.npmjs.com/package/js-reporters)
+[![npm](https://img.shields.io/npm/v/js-reporters.svg)](https://www.npmjs.com/package/js-reporters)
 [![npm](https://img.shields.io/npm/l/js-reporters.svg?maxAge=2592000)](https://www.npmjs.com/package/js-reporters)
 
 The Common Reporter Interface (CRI) for JavaScript Unit Testing Frameworks.