Fix swapped arguments in ThickCircle constructor.
Fix swapped arguments in ThickCircle constructor.

This was a mistake in #646 that I missed.

google/codeworld,google/codeworld,alphalambda/codeworld,pranjaltale16/codeworld,pranjaltale16/codeworld,google/codeworld,alphalambda/codeworld,alphalambda/codeworld,pranjaltale16/codeworld