Fix for test failure with Click 7.0

tests/test_publish_heroku.py

@@ -24,7 +24,7 @@ def test_publish_heroku_installs_plugin(mock_call, mock_check_output, mock_which
     with runner.isolated_filesystem():
         open("t.db", "w").write("data")
         result = runner.invoke(cli.cli, ["publish", "heroku", "t.db"], input="y\n")
-        assert -1 == result.exit_code
+        assert 0 != result.exit_code
     mock_check_output.assert_has_calls(
         [mock.call(["heroku", "plugins"]), mock.call(["heroku", "apps:list", "--json"])]
     )