Added import of MetaData

Author: cdemonchy

sqlacodegen/codegen.py

@@ -635,6 +635,7 @@ def __init__(self, metadata, noindexes=False, noconstraints=False,
                     model.parent_name = parent_name
         else:
             self.collector.add_literal_import('sqlalchemy.ext.declarative', 'declarative_base')
+            self.collector.add_literal_import('sqlalchemy', 'MetaData')
 
     def render(self, outfile=sys.stdout):
         print(self.header, file=outfile)