Revert "Revert behavior of #schema_default from #677"

This reverts commit b51606d.

Author: drwl

lib/annotate/annotate_models.rb

@@ -213,7 +213,7 @@ def quote(value)
     end
 
     def schema_default(klass, column)
-      quote(klass.column_defaults[column.name])
+      quote(klass.columns.find { |x| x.name.to_s == column.name.to_s }.try(:default))
     end
 
     def retrieve_indexes_from_table(klass)