Fix typo in legacy docs (#2037)

uspported -> supported

Co-authored-by: Chalmer Lowe <[email protected]>

Author: jeffqg

docs/bigquery/legacy_proto_types.rst

@@ -3,7 +3,7 @@ Legacy proto-based Types for Google Cloud Bigquery v2 API
 
 .. warning::
     These types are provided for backward compatibility only, and are not maintained
-    anymore. They might also differ from the types uspported on the backend. It is
+    anymore. They might also differ from the types supported on the backend. It is
     therefore strongly advised to migrate to the types found in :doc:`standard_sql`.
 
     Also see the :doc:`3.0.0 Migration Guide<../UPGRADING>` for more information.