Fix missing Semigroup instance for Drawing.
Fix missing Semigroup instance for Drawing.

See #683

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