[SQL] fix typo in class description

[jackylk]

No description provided.

[SparkQA]

Test build #25744 has started for PR 4100 at commit fcc8c85.

• This patch merges cleanly.

[SparkQA]

Test build #25746 has started for PR 4100 at commit b13b9d6.

• This patch merges cleanly.

[rxin]

Thanks. Merging in master.

[SparkQA]

Test build #25744 has finished for PR 4100 at commit fcc8c85.

• This patch fails MiMa tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test FAILed.
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https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/25744/
Test FAILed.

[SparkQA]

Test build #25746 has finished for PR 4100 at commit b13b9d6.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
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Test PASSed.