Use generic badge for Apache License (#144)

Author: wangjoshuah

README.md

@@ -1,7 +1,7 @@
 Optimizely Java SDK
 ===================
 [![Build Status](https://travis-ci.org/optimizely/java-sdk.svg?branch=master)](https://travis-ci.org/optimizely/java-sdk)
-[![Apache 2.0](https://img.shields.io/github/license/nebula-plugins/gradle-extra-configurations-plugin.svg)](http://www.apache.org/licenses/LICENSE-2.0)
+[![Apache 2.0](https://img.shields.io/badge/license-APACHE%202.0-blue.svg)](http://www.apache.org/licenses/LICENSE-2.0)
 
 This repository houses the Java SDK for Optimizely's Full Stack product.