Validate both in and notin the same way

This commit fixes the following error

Model.search_for("id !^ (2,3)") fails with
ScopedSearch::QueryNotSupported: Value '2,3' is not valid for field 'id'

It does it by splitting value for both in and not in

lib/scoped_search/query_builder.rb

@@ -509,7 +509,7 @@ def to_single_field_sql(builder, definition, &block)
           raise ScopedSearch::QueryNotSupported, "Field '#{lhs.value}' not recognized for searching!" unless field
 
           # see if the value passes user defined validation
-          if operator == :in
+          if [:in, :notin].include?(operator)
             rhs.value.split(',').each { |v| validate_value(field, v) }
           else
             validate_value(field, rhs.value)