Update mp_jsonout.sas

mod option added to the file statement in the last %else %if statement (&action=CLOSE) to avoid output file being overwritten

base/mp_jsonout.sas

@@ -165,8 +165,8 @@
 %end;
 
 %else %if &action=CLOSE %then %do;
-  data _null_;file &jref encoding='utf-8';
+  data _null_;file &jref encoding='utf-8' mod;
     put "}";
   run;
 %end;
-%mend;
+%mend;