[DOC] Remove warnings

[barry-jin]

Description

Currently, GluonNLP CI for docs building will always fail because of the following errors. WARNING: the mxtheme extension does not declare if it is safe for parallel reading, assuming it isn't - please ask the extension author to check and make it explicit WARNING: doing serial read We may have two possible solutions.

1. Disable parallel building.
2. Update mxtheme extension to make parallel read safe.

This PR will disable parallel building to remove these warnings.

Checklist

Essentials

• [x] PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• [x] Changes are complete (i.e. I finished coding on this PR)
• [ ] All changes have test coverage
• [ ] Code is well-documented

Changes

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

cc @dmlc/gluon-nlp-team

[codecov[bot]]

Codecov Report

Merging #1428 into master will increase coverage by 0.20%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1428      +/-   ##
==========================================
+ Coverage   85.13%   85.33%   +0.20%     
==========================================
  Files          53       53              
  Lines        6928     6928              
==========================================
+ Hits         5898     5912      +14     
+ Misses       1030     1016      -14     

Impacted Files	Coverage Δ
src/gluonnlp/data/loading.py	83.39% <0.00%> (+5.28%)	:arrow_up:

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[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1428/doc-warning/index.html