[improvement] Slider: support number type of bar-height prop (#3794)

src/slider/test/__snapshots__/index.spec.js.snap

@@ -1,5 +1,15 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`bar height 1`] = `
+<div class="van-slider">
+  <div class="van-slider__bar" style="width: 50%; height: 10px;">
+    <div role="slider" tabindex="0" aria-valuemin="0" aria-valuenow="50" aria-valuemax="100" aria-orientation="horizontal" class="van-slider__button-wrapper">
+      <div class="van-slider__button"></div>
+    </div>
+  </div>
+</div>
+`;
+
 exports[`click bar 1`] = `
 <div class="van-slider van-slider--disabled">
   <div class="van-slider__bar" style="width: 50%; height: 2px;">

src/slider/test/index.spec.js

@@ -105,3 +105,14 @@ it('click vertical', () => {
 
   restoreMock();
 });
+
+it('bar height', () => {
+  const wrapper = mount(Slider, {
+    propsData: {
+      value: 50,
+      barHeight: 10
+    }
+  });
+
+  expect(wrapper).toMatchSnapshot();
+});