Fix problem definition of difference of squares
Fix problem definition of difference of squares

Fixes https://github.com/exercism/exercism.io/issues/1985

petertseng/x-common,kgengler/x-common,ErikSchierboom/x-common,Vankog/problem-specifications,petertseng/x-common,kgengler/x-common,exercism/x-common,wobh/x-common,jmluy/x-common,rpottsoh/x-common,Vankog/problem-specifications,exercism/x-common,rpottsoh/x-common,jmluy/x-common,bennn/x-common,ekse/exercism-common,ErikSchierboom/x-common,jmluy/x-common