update version number in README.md

Author: oschwald

README.md

@@ -23,7 +23,7 @@ To do this, add the dependency to your pom.xml:
     <dependency>
         <groupId>com.maxmind.minfraud</groupId>
         <artifactId>minfraud</artifactId>
-        <version>0.4.0</version>
+        <version>0.5.0</version>
     </dependency>
 ```