Merge pull request #1918 from 3DHubs/fix-textual-coersion

Fix the usage of the deprecated textual coercion in SqlAlchemy 1.3+

flask_admin/contrib/sqla/ajax.py

-from sqlalchemy import or_, and_, cast
+from sqlalchemy import or_, and_, cast, text
 from sqlalchemy.types import String
 
 from flask_admin._compat import as_unicode, string_types
@@ -73,7 +73,7 @@ class QueryAjaxModelLoader(AjaxModelLoader):
         query = query.filter(or_(*filters))
 
         if self.filters:
-            filters = ["%s.%s" % (self.model.__tablename__.lower(), value) for value in self.filters]
+            filters = [text("%s.%s" % (self.model.__tablename__.lower(), value)) for value in self.filters]
             query = query.filter(and_(*filters))
 
         if self.order_by: