[CI] Update MXNet master version tested on CI (#1113)

[eric-haibin-lin]

Description

(Brief description on what this PR is about)

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

cc @dmlc/gluon-nlp-team

[codecov]

Codecov Report

Merging #1176 into v0.9.x will decrease coverage by 0.34%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           v0.9.x   #1176      +/-   ##
=========================================
- Coverage   88.85%   88.5%   -0.35%     
=========================================
  Files          72      72              
  Lines        6970    6970              
=========================================
- Hits         6193    6169      -24     
- Misses        777     801      +24

Impacted Files	Coverage Δ
src/gluonnlp/data/word_embedding_evaluation.py	89.31% <0%> (-7.64%)	⬇️
src/gluonnlp/data/glue.py	96.81% <0%> (-1.82%)	⬇️

[mli]

Job PR-1176/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1176/1/index.html

[leezu]

Is this the nightly build or stable releases

[eric-haibin-lin]

nightly build, i think. @szha please feel free to comment

[leezu]

% md5sum mxnet-1.6.0-py2.py3-none-manylinux1_x86_64.whl                                  ~/src/mxnet-master/build citestcmake ip-172-31-95-96
be9cf7c44761be982e3c47728f0e2bf3  mxnet-1.6.0-py2.py3-none-manylinux1_x86_64.whl

% md5sum mxnet-1.6.0b20200224-py2.py3-none-manylinux1_x86_64.whl                         ~/src/mxnet-master/build citestcmake ip-172-31-95-96
15834d95495f4248b18a9714e5903481  mxnet-1.6.0b20200224-py2.py3-none-manylinux1_x86_64.whl

The link you use doesn't seem to refer to the latest nightly build.

[eric-haibin-lin]

I'm cherry-picking the changes in https://github.com/dmlc/gluon-nlp/pull/1152/files back to v0.9. Should the master branch be updated, too?

[leezu]

The link will need to be updated again.