Bump tensorflow from 1.14 to 2.7.2 in /docs

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.14 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@v1.14.0...v2.7.2)

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

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Author: dependabot[bot]

docs/requirements.txt

@@ -8,7 +8,7 @@ matplotlib
 numpy>=1.16
 pandas
 scipy>=0.17
-tensorflow==1.14
+tensorflow==2.7.2
 xport
 scikit-image
 requests