Fix typo

Author: rdswift

functions/func_dateformat.rst

@@ -49,7 +49,7 @@ The following statements will return the values indicated:
    $dateformat(2021-7-21)                ==>  "2021-07-21"
    $dateformat(2021-7-21,\%B \%d\, \%Y)  ==>  "July 21, 2021"
 
-   $dateformat(2021-07-21,,myd)          ==>  "2021-07-21"
+   $dateformat(2021-07-21,,ymd)          ==>  "2021-07-21"
    $dateformat(2021-07-21,,dmy)          ==>  ""
    $dateformat(2021-07-21,,mdy)          ==>  ""
    $dateformat(2021-July-21)             ==>  ""