docs(build): Update latest docs to v20.03.4.

[danielmai]

Update docs's build.sh to set v20.03.4 as the latest docs.

<!-
Your title must be in the following format: topic(Area): Feature
Topic must be one of build|ci|docs|feat|fix|perf|refactor|chore|test

Sample Titles:
feat(Enterprise): Backups can now get credentials from IAM
fix(Query): Skipping floats that cannot be Marshalled in JSON
perf: [Breaking] json encoding is now 35% faster if SIMD is present
chore: all chores/tests will be excluded from the CHANGELOG

Please add a description with these things:

1. A good description explaining the problem and what you changed.
2. If it fixes any GitHub issues, say "Fixes #GitHubIssue".
3. If it corresponds to a Jira issue, say "Fixes DGRAPH-###".
4. If this is a breaking change, please put "[Breaking]" in the title. In the description, please put a note with exactly who these changes are breaking for.
   -->

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[darkn3rd]

Reviewed 1 of 1 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @MichaelJCompton)