[new feature] normalize size of all icons (#292)

* [bugfix] CouponList always show empty info

* [bugfix] add click feedback of buttons in components

* [Doc] add custom theme document

* [new feature] Notice bar support more props

* [bugfix] PullRefresh test cases

* [bugfix] unused NoticeBar style

* [bugfix] Swipe width calc error

* [Doc] english document of all action components

* [Doc] change document site path to /zanui/vant

* [Doc] fix

* [bugfix] uploader style error

* [bugfix] tabs document demo

* [new feature] Cell support vue-router target route

* [bugfix] add cell test cases

* update yarn.lock

* [bugfix] Tabbar cann't display info when use icon slot

* [Doc] update document title

* [bugfix] Dialog should reset button text when showed

* [new feature] CouponList add showCloseButton prop

* [new feature] Swipe add 'initialSwipe' prop

* [bugfix] NoticeBar text disappeared when page back

* [new feature] ImagePreview support startPosition

* fix: improve imagePreview test cases

* [bugfix] Steps style error when has more than 4 items

* [new feature] normalize size of all icons

packages/vant-css/src/checkbox.css

@@ -9,7 +9,7 @@ $van-checkbox-size: 20px;
     color: $white;
     display: block;
     line-height: 1;
-    font-size: 14px;
+    font-size: 12px;
     text-align: center;
     pointer-events: none;
     border: 1px solid #aaa;