Don't use file name argument to show method

Since 7747261 removed the file name
argument to the show method of GraphicsArray (without deprecatuion
procedure), we should not document it being called in this way.

Instead we can save it to a file (which won't get displayed automatically)
to demonstrate the core idea of specifying a custom file name here.

Author: gagern

src/sage/plot/animate.py

@@ -491,12 +491,12 @@ def graphics_array(self, ncols=3):
             Graphics Array of size 2 x 3
             sage: g.show(figsize=[6,3]) # optional
 
-        Specify different arrangement of array and save with different file name::
+        Specify different arrangement of array and save it with a given file name::
 
             sage: g = a.graphics_array(ncols=2); print g
             Graphics Array of size 2 x 2
             sage: f = tmp_filename(ext='.png')
-            sage: g.show(f) # optional
+            sage: g.save(f) # optional
 
         Frames can be specified as a generator too; it is internally converted to a list::