message: [new feature] Picker: add toolbar-position prop
diff: @@ -16,6 +16,10 @@ export default sfc({
  type: Number,
  default: 0
  },
  + toolbarPosition: {
  + type: String,
  + default: 'top'
  + },
  valueKey: {
  type: String,
  default: 'text'
  @@ -176,7 +180,7 @@ export default sfc({
  return (
  <div class={bem()}>
  - {Toolbar}
  + {this.toolbarPosition === 'top' ? Toolbar : h()}
  {this.loading ? <Loading class={bem('loading')} color={BLUE} /> : h()}
  <div class={bem('columns')} style={columnsStyle} onTouchmove={preventDefault}>
  {columns.map((item, index) => (
  @@ -195,6 +199,7 @@ export default sfc({
  <div class={bem('mask')} style={maskStyle} />
  <div class={['van-hairline--top-bottom', bem('frame')]} style={frameStyle} />
  </div>
  + {this.toolbarPosition === 'bottom' ? Toolbar : h()}
  </div>
  );
  }
  