Update client version string

Author: 17twentynine

api/src/main/java/com/messagebird/MessageBirdServiceImpl.java

@@ -72,7 +72,7 @@ public class MessageBirdServiceImpl implements MessageBirdService {
 
     private final String accessKey;
     private final String serviceUrl;
-    private final String clientVersion = "6.2.2";
+    private final String clientVersion = "6.2.3";
     private final String userAgentString;
     private Proxy proxy = null;