Update numba dependency in setup.py

[leezu]

numba<=0.45.1 is incompatible with numpy>=1.17

cc @dmlc/gluon-nlp-team

[mli]

Job PR-941/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-941/1/index.html

[codecov]

Codecov Report

Merging #941 into master will increase coverage by 0.54%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #941      +/-   ##
==========================================
+ Coverage   90.12%   90.67%   +0.54%     
==========================================
  Files          67       67              
  Lines        6389     6389              
==========================================
+ Hits         5758     5793      +35     
+ Misses        631      596      -35

Impacted Files	Coverage Δ
src/gluonnlp/data/word_embedding_evaluation.py	96.96% <0%> (+0.75%)	⬆️
src/gluonnlp/data/dataset.py	99.2% <0%> (+1.58%)	⬆️
src/gluonnlp/data/batchify/batchify.py	96.59% <0%> (+3.4%)	⬆️
src/gluonnlp/data/transforms.py	81.59% <0%> (+4.59%)	⬆️
src/gluonnlp/data/corpora/wikitext.py	100% <0%> (+5.17%)	⬆️
src/gluonnlp/model/parameter.py	100% <0%> (+8%)	⬆️