Arrow keys don't preserve distance between handles with behaviour drag-fixed

[djast]

With behaviour: 'drag-fixed', the user can still click on a handle and move the sliders further apart using arrow keys.

E.g., at https://refreshless.com/nouislider/behaviour-option/#section-fixed , click the left handle and press the left-arrow key, or click the right handle and click the right-arrow key.

It appears that handles can't be moved closer together than the original distance between them, but they can be moved further apart, at which point dragging either handle moves both handles.