Bump tensorflow from 1.14.0 to 2.4.2

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
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Ch2/ch2-requirements.txt

@@ -5,7 +5,7 @@ nlpaug==0.0.14
 snorkel==0.9.6
 treedlib==0.1.3
 numbskull==0.1.1
-tensorflow==1.15
+tensorflow==2.4.2
 tensorboard==1.15
 nltk==3.2.5
 matplotlib==3.2.2

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

requirements.txt

@@ -150,7 +150,7 @@ summa==1.2.0
 sumy==0.8.1
 tabulate==0.8.7
 tensorboard==1.14.0
-tensorflow==1.14.0
+tensorflow==2.4.2
 tensorflow-estimator==1.14.0
 termcolor==1.1.0
 terminado==0.8.3