[SPARK-16256][DOCS] Minor fixes on the Structured Streaming Programming Guide
[SPARK-16256][DOCS] Minor fixes on the Structured Streaming Programming Guide

Author: Tathagata Das <4330a85689689e23b81e88bdf5853b25c33529eb@gmail.com>

Closes #13978 from tdas/SPARK-16256-1.

(cherry picked from commit 2c3d96134dcc0428983eea087db7e91072215aea)
Signed-off-by: Tathagata Das <4330a85689689e23b81e88bdf5853b25c33529eb@gmail.com>

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