Bump tensorflow from 1.15.4 to 2.7.2

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.15.4 to 2.7.2.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.15.4...v2.7.2)

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

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Author: dependabot[bot]

requirements.txt

@@ -6,7 +6,7 @@ nltk==3.4.5
 numpy==1.22.0
 psycopg2-binary==2.7.7
 scipy==1.2.0
-tensorflow==1.15.4
+tensorflow==2.7.2
 tflearn==0.3.2
 whitenoise==5.0.1
 gunicorn==19.9.0