module Rackup::Handler

def self.pick(server_names)

=> Rackup::Handler::WEBrick
> pick ['puma', 'webrick']

Raises `LoadError` if no handler was found.
Select first available Rack handler given an `Array` of server names. 
def self.pick(server_names)
  server_names = Array(server_names)
  server_names.each do |server_name|
    begin
      server = self.get(server_name)
     return server if server
    rescue LoadError
      # Ignore.
    end
  end
  raise LoadError, "Couldn't find handler for: #{server_names.join(', ')}."
end