Editorial: Fix ecma-262 ref to unify referenced terms list

Author: inexorabletash

index.bs

@@ -32,7 +32,7 @@ spec:dom; type:dfn; text:event
 </pre>
 
 <pre class=anchors>
-spec: ecma262; urlPrefix: https://tc39.github.io/ecma262/
+spec: ecma-262; urlPrefix: https://tc39.github.io/ecma262/
     type: dfn; for: ECMAScript
         url: sec-algorithm-conventions
             text: !