[components][expression_language] Fix the wrong constructor for

SerializedParsedExpression

There is a bug in the code snippet for creating a
SerializedParsedExpression instance in chapter "Using Parsed and
Serialized Expressions"

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

components/expression_language/caching.rst

@@ -65,7 +65,7 @@ Both ``evaluate()`` and ``compile()`` can handle ``ParsedExpression`` and
 
     $expression = new SerializedParsedExpression(
         '1 + 4',
-        serialize($language->parse('1 + 4', array()))
+        serialize($language->parse('1 + 4', array())->getNodes())
     );
 
     echo $language->evaluate($expression); // prints 5