upgrading to tf-gpu

ml-agents/setup.py

         "Pillow>=4.2.1",
         "protobuf>=3.6",
         "pyyaml",
-        "tensorflow>=1.7,<2.0",
+        "tensorflow-gpu==1.15",
         'pypiwin32==223;platform_system=="Windows"',
     ],
     python_requires=">=3.6.1",