Merge: [BERT/TF2] Fix WikiExtractor issue

TensorFlow2/LanguageModeling/BERT/Dockerfile

@@ -22,7 +22,7 @@ ENV HOME /workspace
 
 WORKDIR /workspace
 RUN git clone https://github.com/openai/gradient-checkpointing.git
-RUN git clone https://github.com/attardi/wikiextractor.git
+RUN git clone https://github.com/attardi/wikiextractor.git && cd wikiextractor && git checkout 6408a430fc504a38b04d37ce5e7fc740191dee16 && cd ..
 RUN git clone https://github.com/soskek/bookcorpus.git
 RUN git clone https://github.com/titipata/pubmed_parser