[BUGFIX] Fix glue test result serialization

[eric-haibin-lin]

Description

Make test result.tsv consistent with the format required on GLUEBenchmark.

Checklist

Essentials

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

[mli]

Job PR-773/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-773/1/index.html

[codecov]

Codecov Report

Merging #773 into master will increase coverage by 0.41%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #773      +/-   ##
==========================================
+ Coverage   90.21%   90.63%   +0.41%     
==========================================
  Files          64       64              
  Lines        6233     6233              
==========================================
+ Hits         5623     5649      +26     
+ Misses        610      584      -26

Impacted Files	Coverage Δ
src/gluonnlp/data/stream.py	89.61% <0%> (+0.54%)	⬆️
src/gluonnlp/data/word_embedding_evaluation.py	96.96% <0%> (+0.75%)	⬆️
src/gluonnlp/data/batchify/batchify.py	96.29% <0%> (+1.23%)	⬆️
src/gluonnlp/data/dataset.py	98.41% <0%> (+1.58%)	⬆️
src/gluonnlp/data/transforms.py	80.28% <0%> (+3.01%)	⬆️
src/gluonnlp/data/corpora/wikitext.py	100% <0%> (+5.17%)	⬆️
src/gluonnlp/model/parameter.py	100% <0%> (+8%)	⬆️

[mli]

Job PR-773/2 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-773/2/index.html