Use unique identifiers in example snippet (#185)

Using the same identifier will result in overwriting. The last VH call would win (as described in the next paragraph of the documentation).
Therefore, different identifiers should be used in the example to demonstrate the inclusion of files or inline scripts.

Author: julianhofmann

Documentation/Global/Asset/Script.rst

@@ -19,7 +19,7 @@ Examples
 ::
 
    <f:asset.script identifier="identifier123" src="EXT:my_ext/Resources/Public/JavaScript/foo.js" />
-   <f:asset.script identifier="identifier123">
+   <f:asset.script identifier="identifier987">
       alert('hello world');
    </f:asset.script>