update docs/component/picker.md.

docs/component/picker.md

@@ -218,7 +218,7 @@ export default {
             } else if (type === 'end') {
                 year = year + 2;
             }
-            month = month > 9 ? month : '0' + month;;
+            month = month > 9 ? month : '0' + month;
             day = day > 9 ? day : '0' + day;
             return `${year}-${month}-${day}`;
         }