Shortened line in plotter.py to comply with PEP8

Should rectify tests 36/37

Author: PACarniglia

stonesoup/plotter.py

@@ -220,7 +220,7 @@ def plot_tracks(self, tracks, mapping, uncertainty=False, particle=False, track_
         lines with point markers and default colors. Uncertainty bars are plotted
         with a default color which is the same for all tracks.
 
-        Users can change linestyle, color and marker using keyword arguments. Uncertainty ellipses/bars
+        Users can change linestyle, color and marker using keyword arguments. Uncertainty metrics
         will also be plotted with the user defined colour and any changes will apply to all tracks.
 
         Parameters