Indent license header properly for interfaces.scala.

[rxin]

A very small nit update.

[AmplabJenkins]

Test FAILed.
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[rxin]

Jenkins, retest this please.

[SparkQA]

Test build #24037 has started for PR 3552 at commit df8d1a4.

• This patch merges cleanly.

[SparkQA]

Test build #24037 has finished for PR 3552 at commit df8d1a4.

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

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