fix: export GenerateICS function correctly in calendar.js

src/helpers/calendar.js

@@ -17,7 +17,7 @@ const CREDENTIALS_PATH = path.join(
 );
 
 //generates iCalendar file for a single shift
-GenerateICS = function (shifts) {
+const GenerateICS = function (shifts) {
   // https://stackoverflow.com/questions/3665115/create-a-file-in-memory-for-user-to-download-not-through-server
 
   var content = "BEGIN:VCALENDAR\n";