Changed weights from ints to doubles

ZUNIONSTORE supports double weights, but the api just provides ints for the weights. This is changed by this pull request. Sadly all java redis clients use ints/longs for the weights by now, but even though the clients do not support double weights yet, this should be changed to be able to support double weights in the future. Because double is a superset of int this should not have any negative side effects.

I created a pull request for jedis too, which supports double weights in jedis. A test cases in jedis proves that redis supports double weights. When this pull request has been accepted, the workaround which converts double weights back to ints in the spring jedis adapter has to be removed.