Add npm badge

Author: geowarin

README.md

@@ -1,5 +1,6 @@
 # Friendly-errors-webpack-plugin
 
+[![npm](https://img.shields.io/npm/v/friendly-errors-webpack-plugin.svg)](https://www.npmjs.com/package/friendly-errors-webpack-plugin)
 [![Build Status](https://travis-ci.org/geowarin/friendly-errors-webpack-plugin.svg?branch=master)](https://travis-ci.org/geowarin/friendly-errors-webpack-plugin)
 
 Friendly-errors-webpack-plugin recognizes certain classes of webpack