[SPARK-5478][UI][Minor] Add missing right parentheses

[jerryshao]

[SparkQA]

Test build #26310 has started for PR 4267 at commit 9fe51cc.

• This patch merges cleanly.

[srowen]

Doesn't even need a JIRA, but of course looks fine.

[SparkQA]

Test build #26310 has finished for PR 4267 at commit 9fe51cc.

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

[AmplabJenkins]

Test PASSed.
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https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/26310/
Test PASSed.