[Doc] fix a bug in guide_cn

[PotatoChipsNinja]

Description

Fix a bug in guide_cn

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change,
  or have been fixed to be compatible with this change
• Related issue is referred in this PR
• If the PR is for a new model/paper, I've updated the example index here.

[dgl-bot]

To trigger regression tests:

• @dgl-bot run [instance-type] [which tests] [compare-with-branch];
  For example: @dgl-bot run g4dn.4xlarge all dmlc/master or @dgl-bot run c5.9xlarge kernel,api dmlc/master

[yaox12]

The following pages are missing in guide_cn in comparison to guide:

data-loadcsv.rst
distributed-hetero.rst
minibatch-gpu-sampling.rst
minibatch-prefetching.rst
mixed_precision.rst

Do you have interests to translate them into Chinese?

[PotatoChipsNinja]

The following pages are missing in guide_cn in comparison to guide:

data-loadcsv.rst
distributed-hetero.rst
minibatch-gpu-sampling.rst
minibatch-prefetching.rst
mixed_precision.rst

Do you have interests to translate them into Chinese?

Sorry, I'm not very familiar with DGL yet, maybe someone more experienced can finish it better.

[dgl-bot]

Commit ID: eff17ed

Build ID: 1

Status: ✅ CI test succeeded

Report path: link

Full logs path: link

[dgl-bot]

Commit ID: b5bd872

Build ID: 2

Status: ✅ CI test succeeded

Report path: link

Full logs path: link