Add definition of Slider constructor

bootstrap-slider/bootstrap-slider.d.ts

@@ -137,6 +137,13 @@ interface JQueryEventObject {
     value: number|ChangeValue;
 }
 
+interface SliderStatics {
+	new (selector: string, opts: SliderOptions): Slider;
+	prototype: Slider;
+}
+
+declare var Slider: SliderStatics;
+
 /**
  * This class is actually not used when using the jQuery version of bootstrap-slider
  * The method documentation is still here thouh.