Fix 90 degrees rotation

[nicoeps]

Resolves #781 #990 #1042 #1126 #1278

Rotating clips by either 90 or 270 degrees throws an exception because axes don't match when transposing. The clips seem to contain a frame (particularly the second frame of the clip) that has two dimensions instead of three. These changes should fix this issue by checking the shape for each frame and setting the appropriate value for transposing.

# Code that demonstrates the bug
import moviepy.editor as mp
text_video = mp.TextClip("test", color="blue", fontsize=72)
text_video = text_video.rotate(90).set_duration(2)
text_video.write_videofile("test.mp4", fps=24)

• I have provided code that clearly demonstrates the bug and that only works correctly when applying this fix
• I have added suitable tests demonstrating a fixed bug or new/changed feature to the test suite in tests/
• I have properly documented new or changed features in the documentation or in the docstrings
• I have properly explained unusual or unexpected code in the comments around it
• I have formatted my code using black -t py36

[coveralls]

Coverage remained the same at 67.887% when pulling 44eb1bb on nicoeps:rotate into 4356fcd on Zulko:master.

[tburrows13]

This looks great, thank you so much! You can ignore the failed code format check, that's not your fault (unless you want to work out why it has stopped working for everybody!).

[tburrows13]

There was a merge conflict because I had just merged #1170 which I've now fixed.