Release 1.6.0 and bump version number

Author: zmarkan

README.md

@@ -51,7 +51,7 @@ The pusher-java-client is available in Maven Central.
     <dependency>
       <groupId>com.pusher</groupId>
       <artifactId>pusher-java-client</artifactId>
-      <version>1.5.0</version>
+      <version>1.6.0</version>
     </dependency>
 </dependencies>
 ```

build.gradle

@@ -21,7 +21,7 @@ apply plugin: 'org.ajoberstar.github-pages'
 apply plugin: 'signing'
 
 group = "com.pusher"
-version = "2.0.0-SNAPSHOT"
+version = "1.6.1-SNAPSHOT"
 sourceCompatibility = "1.6"
 targetCompatibility = "1.6"