Passing duration as milliseconds instead of seconds in write_gif_with…

…_image_io. Fixes Zulko#2151.

moviepy/video/io/gif_writers.py

@@ -439,7 +439,7 @@ def write_gif_with_image_io(
     quantizer = 0 if opt != 0 else "nq"
 
     writer = imageio.save(
-        filename, duration=1.0 / fps, quantizer=quantizer, palettesize=colors, loop=loop
+        filename, duration=1000.0 / fps, quantizer=quantizer, palettesize=colors, loop=loop
     )
     logger(message="MoviePy - Building file %s with imageio." % filename)