Bump README version to 5.6

Author: kevinsawicki

README.md

@@ -13,7 +13,7 @@ The http-request library is available from [Maven Central](http://search.maven.o
 <dependency>
  <groupId>com.github.kevinsawicki</groupId>
  <artifactId>http-request</artifactId>
- <version>5.5</version>
+ <version>5.6</version>
 </dependency>
 ```