feat(signature): 签名组件的画布添加白色背景色属性

src/components/Signature/index.js

@@ -81,6 +81,7 @@ function Signature(props) {
             ref={signatureCanvas}
             penColor="black"
             canvasProps={{ width, height }}
+            backgroundColor="rgb(255,255,255)"
             {...restProps}
           />
         </div>