Update CONTRIBUTING.md per @bakkot’s feedback

CONTRIBUTING.md

@@ -209,7 +209,7 @@ function Test262Error(message) {
 
 ## Handling Errors and Negative Test Cases
 
-Expectations for **parsing errors** should be declared using [the `negative` frontmatter flag](#negative). They must also include the exact `throw` statement specified in this example (in order to guarantee that implementations do not execute the code):
+Expectations for **parsing errors** should be declared using [the `negative` frontmatter flag](#negative). They must also include `$DONOTEVALUATE();` (in order to guarantee that implementations do not execute the code):
 
 ```javascript
 /*---