Doubleshot ignores classifier for jar dependencies

This is because jar_resolver passes the "to_s" version of jar dependency to Aether. 
(See doubleshot/resolver/jar_resolver.rb:15): 
```ruby
#...
   def resolve!(dependencies)
        dependencies.each do |dependency|
          @aether.add_artifact dependency.to_s
        end
#...
```

As a result aether cannot find the required artifact (it tries to fetch the version without classifier).