Ensure that slider values from nouislider are valid

According to the nouislider docs, values are float by default, and you
must convert them as desired in the to function.

It seems that Math.round is more appropriate than Math.floor - the slider
value might be just below the appropriate value instead of just above.

packages/controls/src/widget_int.ts

@@ -219,7 +219,7 @@ export abstract class BaseIntSliderView extends DescriptionView {
       direction: orientation === 'horizontal' ? 'ltr' : 'rtl',
       format: {
         from: (value: string): number => Number(value),
-        to: (value: number): number => value,
+        to: (value: number): number => this._validate_slide_value(value),
       },
     });
 
@@ -285,7 +285,7 @@ export abstract class BaseIntSliderView extends DescriptionView {
    * and applying it to the other views on the page.
    */
   _validate_slide_value(x: number): number {
-    return Math.floor(x);
+    return Math.round(x);
   }
 
   $slider: any;