Bump tensorflow in /cmd/suggestion/nas/enas/v1alpha3

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 1.15.2 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@v1.15.2...v1.15.4)

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

cmd/suggestion/nas/enas/v1alpha3/requirements.txt

@@ -1,4 +1,4 @@
 grpcio==1.23.0
 protobuf==3.9.1
 googleapis-common-protos==1.6.0
-tensorflow==1.15.2
+tensorflow==1.15.4