Editorial: Fix typo

spec/calendar.html

@@ -184,7 +184,7 @@ <h1>Calendar Date Records</h1>
     <emu-clause id="sec-temporal-calendar-fields-records">
       <h1>Calendar Fields Records</h1>
       <p>
-        An <dfn variants="Calendar Fields Records">Calendar Fields Record</dfn> is a Record value used to represent full or partial input for a calendar date in a non-ISO 8601 calendar.
+        A <dfn variants="Calendar Fields Records">Calendar Fields Record</dfn> is a Record value used to represent full or partial input for a calendar date in a non-ISO 8601 calendar.
         Calendar Fields Records are produced by several abstract operations, such as ISODateToFields and PrepareCalendarFields, and are passed to abstract operations such as CalendarDateFromFields.
       </p>
       <p>Many of the fields in a Calendar Fields Record have the same meaning as the fields of the same name in Calendar Date Records, but each field in a Calendar Fields Record may additionally be ~unset~ to indicate partial input.</p>