add missing event when tapping on track (#1365)

Author: mendyEdri

src/components/slider/index.js

@@ -405,7 +405,7 @@ export default class Slider extends PureBaseComponent {
     if (this.props.disabled) {
       return;
     }
-    
+    this.onSeekStart();
     this.updateTrackStepAndStyle({nativeEvent});
     this.onSeekEnd();
   };