Fixed timestamp format string

Removed superfluous : from timestamp format string

Author: thormick

doc/Type/DateTime.pod6

@@ -66,7 +66,7 @@ instead of an Instant you can supply an L<Int|/type/Int> as a UNIX timestamp.
 
 You can also supply a L<Str|/type/Str> formatted in ISO 8601 timestamp
 notation or as a full L<RFC 3339|https://tools.ietf.org/html/rfc3339>
-date and time.  Strings should be formatted as C<yyyy-mm-ddThh:mm::ssZ>
+date and time.  Strings should be formatted as C<yyyy-mm-ddThh:mm:ssZ>
 or C<yyyy-mm-ddThh:mm:ss+0100>.  We are somewhat less restrictive than the
 ISO 8601 standard, as we allow Unicode digits and mixing of condensed
 and extended time formats.