fixed DecimalField issue with precision

Author: PeterKharchenko

flask_mongoengine/wtf/orm.py

@@ -146,7 +146,7 @@ def conv_Float(self, model, field, kwargs):
     @converts("DecimalField")
     def conv_Decimal(self, model, field, kwargs):
         self._number_common(model, field, kwargs)
-        return f.DecimalField(**kwargs)
+        return f.DecimalField(places = getattr(field, 'precision', None),**kwargs)
 
     @converts("BooleanField")
     def conv_Boolean(self, model, field, kwargs):