Bug#903064: curvedns FTBFS: update Build-Depends: ruby-ronn -> ronn

[Helmut Grohne]

Package: curvedns
Version: 0.87-4
Severity: serious

Since ronn got split out of ruby-ronn, curvedns fails to build from
source. It was not possible to have ruby-ronn temporarily depend on
ronn, because that would have created a dependency cycle. Please update
Build-Depends and replace ruby-ronn with ronn as curvedns uses the
command line tool.

Helmut