Bump tensorflow-gpu from 1.15.5 to 2.7.2

Bumps [tensorflow-gpu](https://github.com/tensorflow/tensorflow) from 1.15.5 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@v1.15.5...v2.7.2)

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

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Author: dependabot[bot]

requirements.txt

@@ -1,4 +1,4 @@
-tensorflow-gpu==1.15.5
+tensorflow-gpu==2.7.2
 torch==1.2.0
 flair==0.4.3
 numpy==1.17.0