[BUGFIX] Fix vocab determinism in py35

[eric-haibin-lin]

Description

Fixes https://github.com/dmlc/gluon-nlp/issues/1158

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

• [ ] Feature1, tests, (and when applicable, API doc)
• [ ] Feature2, tests, (and when applicable, API doc)

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 #1166 into master will decrease coverage by 17.55%. The diff coverage is 100%.

@@             Coverage Diff             @@
##           master    #1166       +/-   ##
===========================================
- Coverage   88.23%   70.68%   -17.56%     
===========================================
  Files          73       73               
  Lines        6980     6986        +6     
===========================================
- Hits         6159     4938     -1221     
- Misses        821     2048     +1227

Impacted Files	Coverage Δ
src/gluonnlp/vocab/vocab.py	81.68% <100%> (-13.73%)	:arrow_down:
src/gluonnlp/data/batchify/embedding.py	13.7% <0%> (-83.88%)	:arrow_down:
src/gluonnlp/data/candidate_sampler.py	16.32% <0%> (-75.52%)	:arrow_down:
src/gluonnlp/data/datasetloader.py	15.08% <0%> (-70.26%)	:arrow_down:
src/gluonnlp/utils/parallel.py	29.54% <0%> (-68.19%)	:arrow_down:
src/gluonnlp/data/dataloader.py	22.41% <0%> (-65.52%)	:arrow_down:
src/gluonnlp/optimizer/bert_adam.py	22.53% <0%> (-64.79%)	:arrow_down:
src/gluonnlp/metric/length_normalized_loss.py	25% <0%> (-64.29%)	:arrow_down:
src/gluonnlp/utils/parameter.py	24.19% <0%> (-62.91%)	:arrow_down:
src/gluonnlp/loss/activation_regularizer.py	35.48% <0%> (-51.62%)	:arrow_down:
... and 31 more

[mli]

Job PR-1166/1 is complete. Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1166/1/index.html