The problem might be that sqlfiddle does not support this functionality.
Schema's do not seem to be supported, but you can try like this:
create table tmpx (n text, v text, t text[]);
create table tmpy (n text, v text, p text);
delete from tmpx;
delete from tmpy;
insert into tmpx values ('android.apps', '3.1.4', null);
insert into tmpy values ('android.apps', '3.1.4', '08.12.2017');
insert into tmpy values ('android.apps', '3.1.4', '03.12.2017');
UPDATE tmpx set t = sub.t
FROM (select array_agg(p) as t
from tmpy,tmpx where tmpx.n = tmpy.n and tmpx.v = tmpy.v) AS sub;
select * from tmpx;
Also you need to select PostgreSQL 9.6 instead of 9.3