Fix ratis examples after supporting streaming

When run ratis examples , get the following errors.

Found /Users/fermi/projects/incubator-ratis/ratis-examples/target/ratis-examples-1.1.0-SNAPSHOT.jar
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
at org.apache.ratis.examples.common.SubCommandBase.lambda$parsePeers$0(SubCommandBase.java:46)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:546)
at java.util.stream.AbstractPipeline.evaluateToArrayNode(AbstractPipeline.java:260)
at java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:438)
at org.apache.ratis.examples.common.SubCommandBase.parsePeers(SubCommandBase.java:48)
at org.apache.ratis.examples.common.SubCommandBase.getPeers(SubCommandBase.java:52)
at org.apache.ratis.examples.common.SubCommandBase.getPeer(SubCommandBase.java:84)
at org.apache.ratis.examples.arithmetic.cli.Server.run(Server.java:60)
at org.apache.ratis.examples.common.Runner.main(Runner.java:63)