update version number in README.md

Author: oschwald

README.md

@@ -16,7 +16,7 @@ To do this, add the dependency to your pom.xml:
     <dependency>
         <groupId>com.maxmind.db</groupId>
         <artifactId>maxmind-db</artifactId>
-        <version>1.2.0</version>
+        <version>1.2.1</version>
     </dependency>
 ```