bugfix:post-processing script of dynamic cantilever beam

This commit fixes an issue due to matplotlib version. Some versions of
matplotlib for plotting grid line and showing it uses different argument
names. Here since we always want to plot the grid, we remove the
argument to plot the grid line. By default grid lines will be plotted.

examples/DynamicCantileverCase/dynamic_cantilever_post_processing.py

@@ -91,7 +91,7 @@ def plot_end_position_with(
     )
     ax.set_xlabel("Time [s]", fontsize=16)
     ax.set_ylabel("Displacement [m]", fontsize=16)
-    ax.grid(visible=True, which="both", color="k", linestyle="--")
+    ax.grid(which="both", color="k", linestyle="--")
 
     time = np.array(recorded_history["time"])
     positions = analytical_cantilever_soln.get_time_dependent_positions(1, time)