Error in widget option documentation for the date field type

In the date field type documentation for the master branch, it's said that setting the `widget` option to `single_text` causes to display an `input` with a `text` type. I read this and I was about to extend it to have the HTML5 `date` type when I realized that, in fact, `single_text` option gives already a `date` type. I don't know if in previous releases it was that way or not.
