use pure number as option text will cause error

[neoblackcap]

when I use a pure number as the option text in result. select 2 will use toUpCase method first, and a pure number doesn't have it, it will cause error.

[kevin-brown]

The text should be a string (like regular text), same with the id.

We have started enforcing this in 4.0, which you can find at https://github.com/ivaynberg/select2/pull/2743.