List the names of the coins above the average price on April 28, 2013.
average price = divide(sum(price), count(name)); on April 28, 2013 refers to date = '2013-04-28'
SELECT T1.name FROM coins AS T1 INNER JOIN historical AS T2 ON T1.id = T2.coin_id WHERE T2.date = '2018-04-28' AND T2.price > ( SELECT AVG(price) FROM historical WHERE date = '2018-04-28' )