Bump tensorflow-gpu

Bumps [tensorflow-gpu](https://github.com/tensorflow/tensorflow) from 1.12.0 to 1.15.4.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.12.0...v1.15.4)

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Author: dependabot[bot]

tensorflow_classify_text_deploy_algorithmia_simple/model_requirements.txt

@@ -1,3 +1,3 @@
 algorithmia>=1.0.0,<2.0
 six
-tensorflow-gpu==1.12.0
+tensorflow-gpu==1.15.4