doc: Typo in `define-refiner` example
Typo in the #:follows
arg in this example in the Xsmith reference doc:
(define-refiner
arith
prevent-divide-by-zero
...
#:follows:replace-rhs-val-with-zero
Typo in the #:follows
arg in this example in the Xsmith reference doc:
(define-refiner
arith
prevent-divide-by-zero
...
#:follows:replace-rhs-val-with-zero