[improvement] Checkbox: add checked-color prop (#2057)

packages/checkbox/en-US.md

@@ -31,7 +31,14 @@ export default {
 <van-checkbox v-model="checked" disabled>Checkbox</van-checkbox>
 ```
 
+#### Custom Color
+
+```html
+<van-checkbox v-model="checked" checked-color="#4b0">Checkbox</van-checkbox>
+```
+
 #### Custom Icon
+
 Use icon slot to custom icon
 
 ```html
@@ -58,6 +65,7 @@ export default {
 ```
 
 #### Checkbox Group
+
 When Checkboxes are inside a CheckboxGroup, the checked checkboxes's name is an array and bound with CheckboxGroup by v-model.
 
 ```html
@@ -131,11 +139,12 @@ export default {
 | Attribute | Description | Type | Default |
 |------|------|------|------|
 | name | Checkbox name | `any` | - |
+| shape | Can be set to `round` `square` | `String` | `round` |
 | v-model | Check status | `Boolean` | `false` |
 | disabled | Diable checkbox | `Boolean` | `false` |
 | label-disabled | Whether to disable label click | `Boolean` | `false` |
 | label-position | Can be set to `left` | `String` | `right` |
-| shape | Can be set to `round` `square` | `String` | `round` |
+| checked-color | Checked color | `String` | `#1989fa` | - |
 
 ### CheckboxGroup API