remove leftover '='

Author: nicholasshirley

src/ch03-05-control-flow.md

@@ -365,7 +365,7 @@ fn main() {
     while number != 0 {
         println!("{}!", number);
 
-        number = -= 1;
+        number -= 1;
     }
 
     println!("LIFTOFF!!!");