[SCRIPT] fix electra pretraining utils

[szha]

Description

Add the import change was missed when staging my last fix.

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)
• [x] All changes have test coverage
• [x] Code is well-documented

Changes

• [x] Fix electra pretraining script.

cc @dmlc/gluon-nlp-team

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1518/e24775dcbe377f2ac76af3c2fa670c2f3f69474d/index.html

[codecov[bot]]

Codecov Report

Merging #1518 (312e5f3) into master (601c752) will decrease coverage by 0.47%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1518      +/-   ##
==========================================
- Coverage   86.34%   85.87%   -0.48%     
==========================================
  Files          55       55              
  Lines        7513     7396     -117     
==========================================
- Hits         6487     6351     -136     
- Misses       1026     1045      +19     

Impacted Files	Coverage Δ
conftest.py	76.31% <0.00%> (-9.94%)	:arrow_down:
src/gluonnlp/data/loading.py	75.75% <0.00%> (-2.36%)	:arrow_down:
src/gluonnlp/utils/lazy_imports.py	58.42% <0.00%> (-2.25%)	:arrow_down:
src/gluonnlp/utils/misc.py	54.86% <0.00%> (-1.50%)	:arrow_down:
src/gluonnlp/data/tokenizers/spacy.py	65.33% <0.00%> (-0.91%)	:arrow_down:
src/gluonnlp/data/tokenizers/huggingface.py	71.06% <0.00%> (-0.78%)	:arrow_down:
src/gluonnlp/data/tokenizers/jieba.py	73.13% <0.00%> (-0.40%)	:arrow_down:
src/gluonnlp/models/transformer_xl.py	80.48% <0.00%> (-0.39%)	:arrow_down:
src/gluonnlp/models/xlmr.py	87.87% <0.00%> (-0.36%)	:arrow_down:
src/gluonnlp/models/electra.py	76.50% <0.00%> (-0.34%)	:arrow_down:
... and 17 more

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[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1518/312e5f318c181ac8b59210d612f043f25950e802/index.html