Make build pass on JDK11

[eolivelli]

This patch allows you to build KOP on JDK11.

Without this patch the build fails with this error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project kafka-client-factory: Compilation failure: Compilation failure: 
[ERROR] /Users/enrico.olivelli/dev/kop/kafka-client-factory/src/main/java/io/streamnative/kafka/client/api/KafkaClientFactoryImpl.java:[33,20] cannot access org.apache.kafka-1-0-0.clients.producer.KafkaProducer
[ERROR]   class file for org.apache.kafka-1-0-0.clients.producer.KafkaProducer not found
[ERROR] /Users/enrico.olivelli/dev/kop/kafka-client-factory/src/main/java/io/streamnative/kafka/client/api/KafkaClientFactoryImpl.java:[41,20] cannot access org.apache.kafka-1-0-0.clients.consumer.KafkaConsumer
[ERROR]   class file for org.apache.kafka-1-0-0.clients.consumer.KafkaConsumer not found
[ERROR] -> [Help 1]
[ERROR] 

Modifications
do not use '-' in the package name

As I do not have signed an ICLA with this repo, I would like to state explicitly that I am sending this patch according to the terms Apache License v2.

[BewareMyPower]

Thanks for your contribution. It makes sense to me.

But I have a concern that some version number may have two digits like Kafka 0.10.0.0. If we supported these versions in future, what's the best way to name the package? kafka01000?

[BewareMyPower]

BTW, this change could affect the tests. See https://github.com/streamnative/kop/blob/master/kafka-client-api/src/main/java/io/streamnative/kafka/client/api/KafkaVersion.java

[BewareMyPower]

The getStringSerializer and getStringDeserializer should also be modified, for example,

    public String getStringSerializer() {
        /* ... */
        return String.format("org.apache.kafka-%s.common.serialization.StringSerializer", name);
    }

should be modified to

    public String getStringSerializer() {
        /* ... */
        return String.format("org.apache.kafka%s.common.serialization.StringSerializer", name);
    }

It also applies to getStringDeserializer() because they will use the relocated class path to load classes of different Kafka versions.

[BewareMyPower]

Hi @eolivelli , could you apply my comments to fix the broken tests?

[eolivelli]

sure @BewareMyPower
doing it now

[eolivelli]

thank you !