Pooled Client uses subscribe on psubscribe method

Bug
The pooled Redis client is using the wrong method on the psubscribe method which results in a wrong subscription.
Here a code example:

REDIS = Redis::PooledClient.new(host=ENV["REDIS_HOST"], port=ENV["REDIS_PORT"].to_i, pool_size: 5)
REDIS.psubscribe("a*") do |on|
    on.pmessage do |channel|
        puts "Channel: #{channel}"
    end
end

Which results in the following subscription on the Redis server:

➜ redis-cli monitor
[...]
1561661772.372462 [0 127.0.0.1:65063] "SUBSCRIBE" "a*"
[...]

If we now try to publish, for example, the following message, redis-cli publish 'ab' '{"id":199}', the message will not arrive the server as it will only listen for the a* key.

Therefore, we can fix this by changing the following line

crystal-redis/src/redis/pooled_client.cr

Line 60 in 571ea1c

    
           with_pool_connection &.subscribe(*channel_patterns) { |s| callback_setup_block.call(s) }

to

    with_pool_connection &.psubscribe(*channel_patterns) { |s| callback_setup_block.call(s) }

Note the change; &.subscribe to &.psubscribe.
This will now result in a proper listener:

➜ redis-cli monitor
[...]
1561662810.158611 [0 127.0.0.1:65144] "PSUBSCRIBE" "a*"
[...]

Code reference

  def subscribe(*channels, &callback_setup_block : Redis::Subscription ->)
    with_pool_connection &.subscribe(*channels) { |s| callback_setup_block.call(s) }
  end

  def psubscribe(*channel_patterns, &callback_setup_block : Redis::Subscription ->)
    with_pool_connection &.subscribe(*channel_patterns) { |s| callback_setup_block.call(s) }
  end

Fixed by #85