Fix version check in train_gnmt.py and train_transformer.py

[leezu]

Description

Fix version check in train_gnmt.py and train_transformer.py

Fixes #1002

cc @dmlc/gluon-nlp-team

[codecov]

Codecov Report

Merging #1003 into master will increase coverage by 0.56%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1003      +/-   ##
==========================================
+ Coverage   89.29%   89.85%   +0.56%     
==========================================
  Files          67       67              
  Lines        6351     6351              
==========================================
+ Hits         5671     5707      +36     
+ Misses        680      644      -36

Impacted Files	Coverage Δ
src/gluonnlp/model/attention_cell.py	95.06% <0%> (+1.23%)	⬆️
src/gluonnlp/model/block.py	53.19% <0%> (+2.12%)	⬆️
src/gluonnlp/model/transformer.py	91.31% <0%> (+4.5%)	⬆️
src/gluonnlp/model/seq2seq_encoder_decoder.py	75.38% <0%> (+29.23%)	⬆️

[mli]

Job PR-1003/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-1003/1/index.html