Fix typo in test in 0c2fa43.

Author: samth

math-test/math/tests/number-theory-tests.rkt

@@ -258,7 +258,7 @@
 (check-equal? (modular-expt 3 -2 47) 21)  ; PowerMod[3,-2,47]
 (check-equal? (modular-expt 3 -4 47) 18)  ; PowerMod[3,-4,47]
 
-(check-equal (with-modulus 19 (modexpt 2 -1)) 10)
+(check-equal? (with-modulus 19 (modexpt 2 -1)) 10)
 
 ; "quadratic-residues.rkt"
 (check-equal? (quadratic-character  2 5) -1)