setup.py: not test_requires but tests_require.

even though there are install_requires and setup_requires...

setup.py

@@ -217,6 +217,6 @@ setup(name=name,
         ],
       },
       test_suite='slapos.test',
-      test_requires=[ 'jsonschema' ],
+      tests_require=[ 'jsonschema' ],
     )