added argument for off screen (#1125)

Co-authored-by: Paul Profizi <[email protected]>

Author: ayush-kumar-423

examples/02-modal_analyses/01-plot_and_animate_modes.py

@@ -48,6 +48,7 @@
 
 ###############################################################################
 # Animate a mode shape
+# To suppress window pop-up, set the `off_screen` argument to True.
 # ~~~~~~~~~~~~~~~~~~~~
 
-animation.animate_mode(disp, mode_number=1, save_as="tmp.gif")
+animation.animate_mode(disp, mode_number=1, save_as="tmp.gif", off_screen=True)