Fix typo

backend/scripts/time_residuals.py

@@ -75,7 +75,7 @@ def main():
                         histtype='step',
                         lw=2,
                         label=f'DU {du}',
-                        density=true,
+                        density=True,
                         color=linestyle[0],
                         linestyle=linestyle[1])
             ax.legend(loc='upper right')