pass symbol, not procedure

can't match a procedure

Author: votroto

labs/lab06.md

@@ -77,8 +77,8 @@ consisting of numbers 1,2,3,4,5,6,7 with 4 being the active number.
 ```racket
 (define t (tape '(3 2 1) 4 '(5 6 7)))
 
-(change - t) => '(tape (3 2 1) 3 (5 6 7))
-(change + t) => '(tape (3 2 1) 5 (5 6 7))
+(change '- t) => '(tape (3 2 1) 3 (5 6 7))
+(change '+ t) => '(tape (3 2 1) 5 (5 6 7))
 (move 'left t) => '(tape (2 1) 3 (4 5 6 7))
 (move 'right t) => '(tape (4 3 2 1) 5 (6 7))
 ```