another pass on code style

@manishamde , this PR contains no code changes. For code styles, I did the following:

1. Put a space after `,`.
2. Use `===` instead of `==` in tests.
3. Remove space before `:`.
4. 4-space indentation for method declaration.

Please follow Spark's code style guide for your next contribution! I'm looking forward to it ~ :)

I will send other comments to your PR at apache/spark.