Bump tensorflow from 1.13.0 to 1.15.0 in /Baselines/streaming_sparse_gp

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.13.0 to 1.15.0.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](https://github.com/tensorflow/tensorflow/commits/v1.15.0)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Baselines/streaming_sparse_gp/requirements.txt

@@ -30,7 +30,7 @@ six==1.13.0
 sklearn==0.0
 SQLAlchemy==1.3.11
 tensorboard==1.14.0
-tensorflow==1.13.0
+tensorflow==1.15.0
 tensorflow-estimator==1.14.0
 termcolor==1.1.0
 Werkzeug==0.16.0