Invalid type for tagger option: Proc

[hwhelchel]

@ngs thanks for making a great extension for middleman!

I'm trying to use the lambda tagger like so:

activate :similar, tagger: ->(resource) { [resource.data.category] }

But I'm getting an error:

/Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-blog-similar-2.0.1/lib/middleman-blog-similar/extension.rb:31:in `after_configuration': Invalid type for tagger option: Proc (RuntimeError)
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-core-4.2.1/lib/middleman-core/extension.rb:405:in `block in bind_after_configuration'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-core-4.2.1/lib/middleman-core/callback_manager.rb:57:in `instance_exec'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-core-4.2.1/lib/middleman-core/callback_manager.rb:57:in `block in execute'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/hamster-3.0.0/lib/hamster/vector.rb:1316:in `each'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/hamster-3.0.0/lib/hamster/vector.rb:1316:in `traverse_depth_first'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/hamster-3.0.0/lib/hamster/vector.rb:431:in `each'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-core-4.2.1/lib/middleman-core/callback_manager.rb:57:in `execute'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/contracts-0.13.0/lib/contracts/method_reference.rb:43:in `send_to'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/contracts-0.13.0/lib/contracts/call_with.rb:76:in `call_with'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/contracts-0.13.0/lib/contracts/method_handler.rb:138:in `block in redefine_method'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-core-4.2.1/lib/middleman-core/callback_manager.rb:28:in `block in install_methods!'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-core-4.2.1/lib/middleman-core/application.rb:306:in `initialize'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-cli-4.2.1/bin/middleman:49:in `new'
from /Users/harry/.rbenv/versions/2.3.3/lib/ruby/gems/2.3.0/gems/middleman-cli-4.2.1/bin/middleman:49:in `<top (required)>'
from /Users/harry/.rbenv/versions/2.3.3/bin/middleman:22:in `load'
from /Users/harry/.rbenv/versions/2.3.3/bin/middleman:22:in `<main>'

Is this feature supported still?