Update to latest release, which is 1.7.5

Author: jfarcand

README.md

@@ -10,7 +10,7 @@ Async Http Client library purpose is to allow Java applications to easily execut
  <dependency>
  <groupId>com.ning</groupId>
  <artifactId>async-http-client</artifactId>
- <version>1.7.4</version>
+ <version>1.7.5</version>
  </dependency>
 ```