build(deps): bump tensorflow-gpu from 1.14.0 to 1.15.2

Bumps [tensorflow-gpu](https://github.com/tensorflow/tensorflow) from 1.14.0 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@v1.14.0...v1.15.2)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -41,7 +41,7 @@ six==1.14.0
 stable-baselines==2.10.0
 tensorboard==1.14.0
 tensorflow-estimator==1.14.0
-tensorflow-gpu==1.14.0
+tensorflow-gpu==1.15.2
 termcolor==1.1.0
 traitlets==4.3.3
 wcwidth==0.1.9