Correct the $negate example

Author: michaelhkay

specifications/xpath-functions-40/src/function-catalog.xml

@@ -21616,7 +21616,9 @@ return $norm('data-base') eq $norm('DATABASE')</eg></fos:expression>
                   <fos:result>true()</fos:result>
                </fos:test>
                <fos:test>
-                  <fos:expression><eg>let $negate($predicate) := compose(($predicate, not#1))
+                  <fos:expression><eg>let $negate := fn($predicate) { 
+   compose(($predicate, not#1))
+}   
 return filter(("tic", "tac", "toe"), $negate(contains(?, "a")))</eg></fos:expression>
                   <fos:result>"tic", "toe"</fos:result>
                </fos:test>