Fix varibable name in XML parsing scenario

In the xmltodict example, the xml is loaded in the variable obj but is later referenced as doc.
Fixed by renaming obj to doc

docs/scenarios/xml.rst

@@ -59,7 +59,7 @@ can be loaded into a Python dict like this:
     import xmltodict
 
     with open('path/to/file.xml') as fd:
-        obj = xmltodict.parse(fd.read())
+        doc = xmltodict.parse(fd.read())
 
 and then you can access elements, attributes and values like this: