Update time.go

Signed-off-by: Carl Vincent <carlv@stripe.com>

time.go

@@ -76,6 +76,8 @@ const (
 	ISO8601TimeWithReducedPrecisionLocaltime = "2006-01-02T15:04"
 	// ISO8601TimeUniversalSortableDateTimePattern represents a ISO8601 universal sortable date time pattern.
 	ISO8601TimeUniversalSortableDateTimePattern = "2006-01-02 15:04:05"
+	// short form of ISO8601TimeUniversalSortableDateTimePattern
+	ISO8601TimeUniversalSortableDateTimePatternShortForm = "2006-01-02"
 	// DateTimePattern pattern to match for the date-time format from http://tools.ietf.org/html/rfc3339#section-5.6
 	DateTimePattern = `^([0-9]{2}):([0-9]{2}):([0-9]{2})(.[0-9]+)?(z|([+-][0-9]{2}:[0-9]{2}))$`
 )
@@ -84,7 +86,7 @@ var (
 	rxDateTime = regexp.MustCompile(DateTimePattern)
 
 	// DateTimeFormats is the collection of formats used by ParseDateTime()
-	DateTimeFormats = []string{RFC3339Micro, RFC3339MicroNoColon, RFC3339Millis, RFC3339MillisNoColon, time.RFC3339, time.RFC3339Nano, ISO8601LocalTime, ISO8601TimeWithReducedPrecision, ISO8601TimeWithReducedPrecisionLocaltime, ISO8601TimeUniversalSortableDateTimePattern}
+	DateTimeFormats = []string{RFC3339Micro, RFC3339MicroNoColon, RFC3339Millis, RFC3339MillisNoColon, time.RFC3339, time.RFC3339Nano, ISO8601LocalTime, ISO8601TimeWithReducedPrecision, ISO8601TimeWithReducedPrecisionLocaltime, ISO8601TimeUniversalSortableDateTimePattern, ISO8601TimeUniversalSortableDateTimePatternShortForm}
 
 	// MarshalFormat sets the time resolution format used for marshaling time (set to milliseconds)
 	MarshalFormat = RFC3339Millis