Fix doc on Channel.subscribed?/2
Fix doc on Channel.subscribed?/2

[ci skip]

waffleio/poxa,joshk/poxa,RobertoSchneiders/poxa,edgurgel/poxa,waffleio/poxa,joshk/poxa,edgurgel/poxa,RobertoSchneiders/poxa,edgurgel/poxa