Bump tensorflow from 1.14.0 to 2.4.2 in /Ch4

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.14.0 to 2.4.2.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.14.0...v2.4.2)

---
updated-dependencies:
- dependency-name: tensorflow
  dependency-type: direct:production
...

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Author: dependabot[bot]

Ch4/ch4-requirements.txt

@@ -5,7 +5,7 @@ nltk==3.5
 gensim==3.8.3
 wget==3.2
 fasttext==0.9.2
-tensorflow==1.14.0
+tensorflow==2.4.2
 torch==1.9.0
 pytorch_pretrained_bert==0.6.2
 tqdm==4.41.1