[hotfix][python] Fix the package name of PythonGatewayServer

[dianfu]

What is the purpose of the change

The package name of PythonGatewayServer has been changed to org.apache.flink.client.python.PythonGatewayServer. It is should be corrected in ProgramOptions.java.

Brief change log

• Correct the package name of PythonGatewayServer used in ProgramOptions to org.apache.flink.client.python

Verifying this change

This change is a trivial rework without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

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Automated Checks

Last check on commit 8ba4d8f (Tue Aug 06 15:59:14 UTC 2019)

Warnings:

• No documentation files were touched! Remember to keep the Flink docs up to date!

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Review Progress

• ❓ 1. The [description] looks good.
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• ❓ 5. Overall code [quality] is good.

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CI report:

• 8ba4d8f : SUCCESS Build

[sunjincheng121]

Thanks for the fix @dianfu
Merging...