chore(deps): Bump tensorflow-gpu (kubeflow#1034)

Bumps [tensorflow-gpu](https://github.com/tensorflow/tensorflow) from 1.15.0 to 1.15.2.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v1.15.0...v1.15.2)

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examples/v1alpha3/NAS-training-containers/RL-cifar10/requirements-gpu.txt

@@ -1,2 +1,2 @@
-tensorflow-gpu==1.15.0
+tensorflow-gpu==1.15.2
 keras==2.2.4