Minor fix for zooming

It's weird that when you Scroll Up, the interactive shell zooms out.

So to fix this replace factor -> 1/factor .

manimlib/scene/scene.py

@@ -570,7 +570,7 @@ class Scene(object):
         frame = self.camera.frame
         if self.window.is_key_pressed(ord("z")):
             factor = 1 + np.arctan(10 * offset[1])
-            frame.scale(factor, about_point=point)
+            frame.scale(1/factor, about_point=point)
         else:
             transform = frame.get_inverse_camera_rotation_matrix()
             shift = np.dot(np.transpose(transform), offset)