README.md: set gradle dependency to 3.1.1

Author: greenrobot

README.md

@@ -64,15 +64,15 @@ Add EventBus to your project
 
 Via Gradle:
 ```gradle
-compile 'org.greenrobot:eventbus:3.1.0-RC'
+compile 'org.greenrobot:eventbus:3.1.1'
 ```
 
 Via Maven:
 ```xml
 <dependency>
     <groupId>org.greenrobot</groupId>
     <artifactId>eventbus</artifactId>
-    <version>3.1.0-RC</version>
+    <version>3.1.1</version>
 </dependency>
 ```