Let's change that to the new rubocop default, which is also the
suggestion in the ruby style guide.
See https://github.com/bbatsov/ruby-style-guide#percent-literal-braces
This was changed in diaspora too, see diaspora/diaspora#7466
It also includes the changes in the code. This was done with
`rubocop --auto-correct` and no we have zero offenses again.
Rails logs the content of received json as parameters, but this is a bad
idea for federation messages. It only makes the logfiles bigger without
any benefit, because it's encrypted anyway ...
