Currently not working for Redmine 5.x

Plugin won't install. 

So far we noted that 

-  the  acts-as-taggable-on gem needed was set to a version that was differing from other plugin we were using.
-  issue with "NameError: uninitialized constant Rake::TestTask" which seems to have to do with new Rails version.

I suspect someone with minimal Ruby knowledge could fix .
