Update communities.md to reference 'Hive', 'Hive Power' and 'Hive.blog'...

Update communities.md to reference 'Hive', 'Hive Power' and 'Hive.blog' instead of 'Steem', 'Steem Power' and 'Steemit.com'

I left the reference to the 2017 roadmap pdf on steem.io , but ideally this should be updated too..

changed target branch from master to develop

merged

mentioned in commit e099f0ed