write_gif() ImageMagick fix

[KiLLAAA]

write_gif() fuzz argument had no visible influence on output file due to wrong order of params passsed to ImageMagick, these changes fixed this issue. Optimizations work now too.
Changes are made accordingly to ImageMagick usage documentation.
test snippet:
`
from moviepy.editor import *

clip = (VideoFileClip(infile, audio=False))
clip.write_gif('test.gif', fps=15, program='ImageMagick', fuzz=40, opt='optimize-frame')
`

• If this is a bugfix, I have provided code that clearly demonstrates the problem and that works when used with this PR
• I have added a test to the test suite, if necessary
• I have properly documented new or changed features in the documention, or the docstrings
• I have properly documented unusual changes to the code in the comments around it
• I have made note of any breaking/backwards incompatible changes