[DOC] Add JMLR bib

[astonzhang]

Description

(Brief description on what this PR is about)

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] Add bib entry

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 #1153 into master will increase coverage by 11.85%. The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #1153       +/-   ##
===========================================
+ Coverage   76.09%   87.94%   +11.85%     
===========================================
  Files          72       72               
  Lines        6970     6970               
===========================================
+ Hits         5304     6130      +826     
+ Misses       1666      840      -826

Impacted Files	Coverage Δ
src/gluonnlp/model/attention_cell.py	87.7% <0%> (-2.8%)	:arrow_down:
src/gluonnlp/model/block.py	51.06% <0%> (-2.13%)	:arrow_down:
src/gluonnlp/data/word_embedding_evaluation.py	89.31% <0%> (+0.38%)	:arrow_up:
src/gluonnlp/model/utils.py	73.07% <0%> (+0.76%)	:arrow_up:
src/gluonnlp/model/train/embedding.py	87.17% <0%> (+2.56%)	:arrow_up:
src/gluonnlp/embedding/token_embedding.py	91.79% <0%> (+2.82%)	:arrow_up:
src/gluonnlp/utils/files.py	45.9% <0%> (+3.27%)	:arrow_up:
src/gluonnlp/model/seq2seq_encoder_decoder.py	50% <0%> (+3.33%)	:arrow_up:
src/gluonnlp/vocab/elmo.py	96.66% <0%> (+3.33%)	:arrow_up:
src/gluonnlp/data/dataset.py	98.63% <0%> (+3.4%)	:arrow_up:
... and 14 more

[mli]

Job PR-1153/1 is complete. Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1153/1/index.html