RATIS-1755. Update version number after 2.4.1 release

[adoroszlai]

What changes were proposed in this pull request?

Bump version number in POMs on branch-2 after release.

https://issues.apache.org/jira/browse/RATIS-1755

How was this patch tested?

$ mvn -DskipTests clean package
...
[INFO] Reactor Summary for Apache Ratis 2.4.2-SNAPSHOT:
[INFO] 
[INFO] Apache Ratis ....................................... SUCCESS [  0.776 s]
[INFO] Apache Ratis Documentation ......................... SUCCESS [  0.204 s]
[INFO] Apache Ratis Protocols ............................. SUCCESS [  2.565 s]
[INFO] Apache Ratis Common ................................ SUCCESS [  1.289 s]
[INFO] Apache Ratis Client ................................ SUCCESS [  0.666 s]
[INFO] Apache Ratis Server API ............................ SUCCESS [  0.538 s]
[INFO] Apache Ratis Metrics ............................... SUCCESS [  0.652 s]
[INFO] Apache Ratis Server ................................ SUCCESS [  2.232 s]
[INFO] Apache Ratis - Resource Bundle ..................... SUCCESS [  0.048 s]
[INFO] Apache Ratis gRPC Support .......................... SUCCESS [  0.940 s]
[INFO] Apache Ratis Netty Support ......................... SUCCESS [  0.854 s]
[INFO] Apache Ratis Shell ................................. SUCCESS [  0.673 s]
[INFO] Apache Ratis Test .................................. SUCCESS [  1.119 s]
[INFO] Apache Ratis Tools ................................. SUCCESS [  0.293 s]
[INFO] Apache Ratis Examples .............................. SUCCESS [  2.609 s]
[INFO] Apache Ratis Replicated Map ........................ SUCCESS [  0.047 s]
[INFO] Apache Ratis Project Assembly ...................... SUCCESS [  1.609 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS

[szetszwo]

+1 the change looks good.

[adoroszlai]

Thanks @szetszwo for reviewing and committing it.