Bump tensorflow in /machine-learning/nlp/text-generator

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.0.3 to 2.4.0.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.0.3...v2.4.0)

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Author: dependabot[bot]

machine-learning/nlp/text-generator/requirements.txt

@@ -1,4 +1,4 @@
 numpy
-tensorflow==2.0.3
+tensorflow==2.4.0
 requests
 tqdm