[Python] Fix error in schema examples (pa.unify_schemas) for dev arrow version (#333)

This PR closes https://github.com/apache/arrow-cookbook/issues/331
diff --git a/python/source/schema.rst b/python/source/schema.rst
index e73dbfe..561c3ff 100644
--- a/python/source/schema.rst
+++ b/python/source/schema.rst
@@ -211,7 +211,7 @@
 
     try:
         union_schema =  pa.unify_schemas([first_schema, second_schema, third_schema])
-    except pa.ArrowInvalid as e:
+    except (pa.ArrowInvalid, pa.ArrowTypeError) as e:
         print(e)
 
 .. testoutput::