Typo in the Java example (space after -D)

[charleswang007]

In https://github.com/Azure/azure-event-hubs-for-kafka/tree/master/quickstart/java,

mvn exec:java -Dexec.mainClass="TestProducer"
should be
mvn exec:java -D exec.mainClass="TestProducer"

and

mvn exec:java -Dexec.mainClass="TestConsumer"
should be
mvn exec:java -D exec.mainClass="TestConsumer"

[mjlally07]

Driving me nuts running from VS Code in windows until I found this https://stackoverflow.com/questions/64299956/unknown-lifecycle-phase-on-maven -- need extra quotes for windows (i.e., mvn exec:java -D"exec.mainClass"="TestProducer")