Bump tensorflow-gpu from 1.15.0 to 1.15.2

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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Author: dependabot[bot]

requirements.txt

@@ -9,7 +9,7 @@ fastText==0.9.1
 twitterapi==2.5.9
 simplejson==3.16.0
 xarray==0.12.1
-tensorflow-gpu==1.15.0
+tensorflow-gpu==1.15.2
 pytorch==1.0.1
 dask==2.3.0
 matplotlib==3.1.1