README.md: 2.3 -> 2.4

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1845243 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/README.md b/README.md
index d1102cb..75244c3 100644
--- a/README.md
+++ b/README.md
@@ -66,7 +66,7 @@
 <dependency>
   <groupId>org.apache.commons</groupId>
   <artifactId>commons-configuration2</artifactId>
-  <version>2.3</version>
+  <version>2.4</version>
 </dependency>
 ```