fix(watermark): css variables change

src/packages/__VUE/watermark/doc.en-US.md

@@ -131,4 +131,4 @@ The component provides the following CSS variables, which can be used to customi
 
 | Name | Default Value | 
 | --------------------------------------- | -------------------------- | 
-| --nut-watermark-z-index        | _ 2000_        | 
+| --nut-watermark-z-index        | _2000_        | 

src/packages/__VUE/watermark/doc.md

@@ -136,6 +136,6 @@ app.use(Watermark);
 
 | 名称                                    | 默认值                     | 
 | --------------------------------------- | -------------------------- | 
-| --nut-watermark-z-index        | _ 2000_        | 
+| --nut-watermark-z-index        | _2000_        | 
 
 

src/packages/__VUE/watermark/doc.taro.md

@@ -136,6 +136,6 @@ app.use(Watermark);
 
 | 名称                                    | 默认值                     | 
 | --------------------------------------- | -------------------------- | 
-| --nut-watermark-z-index        | _ 2000_        |
+| --nut-watermark-z-index        | _2000_        |