[hotfix] [flink-examples-streaming] Fix some typos

[wangxianghu]

What is the purpose of the change

Fix some typos in flink-examples-streaming

Brief change log

Fix some typos in flink-examples-streaming

Verifying this change

This change is a trivial rework / code cleanup 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 / docs / JavaDocs / not documented)

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Automated Checks

Last check on commit 059e816 (Wed Feb 12 12:05:14 UTC 2020)

Warnings:

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Review Progress

• ❓ 1. The [description] looks good.
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• ❓ 3. Needs [attention] from.
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• ❓ 5. Overall code [quality] is good.

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CI report:

• 578e142 Travis: FAILURE

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[rmetzger]

Thanks a lot for your hotfix!

Merging this ...