Use better example for Date.new(Instant)

- it's not obvious that `now` is an Instant
- some may wonder how to turn a Unix time stamp into Date

doc/Type/Date.pod6

@@ -48,7 +48,7 @@ or DateTime object.  Optionally accepts a formatter as a named parameter.
     my $date = Date.new(2042, 1, 1);
     $date = Date.new(year => 2042, month => 1, day => 1);
     $date = Date.new("2042-01-01");
-    $date = Date.new(now);
+    $date = Date.new(Instant.from-posix: 1482155532);
     $date = Date.new(DateTime.now);
 
 =head2 method new-from-daycount