[SPARK-30731] Update deprecated Mkdocs option

[nchammas]

Split from #27534.

What changes were proposed in this pull request?

This PR updates a deprecated Mkdocs option to use the new name.

Why are the changes needed?

This change will prevent the docs from failing to build when we update to a version of Mkdocs that no longer supports the deprecated option.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

I built the docs locally and reviewed them in my browser.

[SparkQA]

Test build #118651 has finished for PR 27626 at commit 55b01d3.

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

[HyukjinKwon]

LGTM

[HyukjinKwon]

Thanks, merged to master, branch-3.0 and branch-2.4.

[dongjoon-hyun]

@nchammas . You should use a new JIRA ID because the scope is completely different.

This patch lands branch-2.4 while SPARK-30731 is Improvement JIRA.

[nchammas]

This PR was split from #27534, and the referenced JIRA covers removing deprecated options related to building the docs. So the scope of the JIRA is fine, IMO, and includes this PR.

I'm not sure why this patch was backported to branch-2.4. If you prefer, I can create a new JIRA just for this PR and update the PR title accordingly. Let me know what you want to do.

[srowen]

I think this is OK for a backport, as it is a potential 'fix', is quite minor, and in any event only affects doc gen. Any problem it would cause would be obvious at docs build time.

[dongjoon-hyun]

Yes, @srowen . The individual PR is okay for backporting.

The problem at that time was that @nchammas had three independent PRs had the same JIRA ID (SPARK-30731) while he split one PR to three PRs.

• Since this is merged first for master/3.0/2.4. I switch SPARK-30731 for this PR.
• For the other two PRs, I created separate JIRAs and updated the PR titles like [SPARK-30880][DOCS] Delete Sphinx Makefile cruft.

[HyukjinKwon]

Yes, I couldn't notice this links the same JIRA. Thanks for correcting it @dongjoon-hyun

[HyukjinKwon]

Also, I tested and verified it works, with Python 2.7, in mkdocs 0.17 (2017-10-19) which is before Spark 2.3 (2018-02-28). This mkdocs dependency was added as of Spark 2.3 (SPARK-21485).
This pages was deprecated in Mkdocs 1.0.0 (2018-08-03). Spark 2.4.0 release was 2018-11-02.

If a release manager uses the same machine with the same environment used in Spark 2.3 for Spark 3.0 or 2.4 release, it will still work, unofficially though.

If a release manager uses the same machine with the same environment used in Spark 2.4 for Spark 3.0 or Spark 2.4.x, it will work officially.

So, I think technically there is virtually no overhead.