修复日期公式错误

src/function/functionImplementation.js

@@ -11662,7 +11662,7 @@ const functionImplementation = {
             }
             var date = ""
             // 判断传入的值的类型
-            if(typeof v == 'string') {
+            if(typeof start_date == 'string') {
                 // v为类似与2020-01-01的字符串
                 date = dayjs(start_date).add(months, 'months');
             } else {