[MINOR][PYSPARK][DOC] Fix wrongly formatted examples in PySpark documentation

## What changes were proposed in this pull request?

This PR fixes wrongly formatted examples in PySpark documentation as below:

- **`SparkSession`**

  - **Before**

    ![2016-07-06 11 34 41](https://cloud.githubusercontent.com/assets/6477701/16605847/ae939526-436d-11e6-8ab8-6ad578362425.png)

  - **After**

    ![2016-07-06 11 33 56](https://cloud.githubusercontent.com/assets/6477701/16605845/ace9ee78-436d-11e6-8923-b76d4fc3e7c3.png)

- **`Builder`**

  - **Before**
    ![2016-07-06 11 34 44](https://cloud.githubusercontent.com/assets/6477701/16605844/aba60dbc-436d-11e6-990a-c87bc0281c6b.png)

  - **After**
    ![2016-07-06 1 26 37](https://cloud.githubusercontent.com/assets/6477701/16607562/586704c0-437d-11e6-9483-e0af93d8f74e.png)

This PR also fixes several similar instances across the documentation in `sql` PySpark module.

## How was this patch tested?

N/A

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #14063 from HyukjinKwon/minor-pyspark-builder.