[SPARK-19444][ML][DOCUMENTATION] Fix imports not being present in documentation

## What changes were proposed in this pull request?

SPARK-19444 imports not being present in documentation

## How was this patch tested?

Manual

## Disclaimer

Contribution is original work and I license the work to the project under the project’s open source license

Author: Aseem Bansal <anshbansal@users.noreply.github.com>

Closes #16789 from anshbansal/patch-1.

(cherry picked from commit aee2bd2c)
Signed-off-by: Sean Owen <sowen@cloudera.com>