Fixes an old FRAME_HEIGHT reference

Author: XorUnison

manim/camera/moving_camera.py

@@ -36,7 +36,7 @@ def __init__(self, frame=None, **kwargs):
         """
         digest_config(self, kwargs)
         if frame is None:
-            frame = ScreenRectangle(height=FRAME_HEIGHT)
+            frame = ScreenRectangle(height=config['frame_height'])
             frame.set_stroke(
                 self.default_frame_stroke_color,
                 self.default_frame_stroke_width,