tests: fix test_plot_filter() to make a plot with data

The test for LinePlot with no pivot and filters uses a filter that
leaves the dataframe empty.  Change the filter so that it actually
simulates creating a plot with actual data.
diff --git a/tests/test_plotter.py b/tests/test_plotter.py
index ae59384..4276834 100644
--- a/tests/test_plotter.py
+++ b/tests/test_plotter.py
@@ -67,7 +67,7 @@
                           trace2],
                          [trappy.cpu_power.CpuOutPower],
                          column=["power"],
-                         filters={"cdev_state": [1]})
+                         filters={"cdev_state": [0]})
         l.view(test=True)
 
     def test_plot_pivot(self):