2.11.2 breaks config.ru compatibility

[tomquas]

am using foreman and a very basic config/puma/development.rb to start my app.
my config.ru's first line is '#\ -s puma'.
upgrading from 2.11.1 errors out; see trace below.
removing that line from config.ru fixes the startup process

10:12:10 app.1        | [2514] ! Unable to load application: NoMethodError: undefined method `start_with?' for :server:Symbol
10:12:10 app.1        | /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/configuration.rb:107:in `block in load_rackup': undefined method `start_with?' for :server:Symbol (NoMethodError)
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/configuration.rb:105:in `each'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/configuration.rb:105:in `each_with_object'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/configuration.rb:105:in `load_rackup'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/configuration.rb:69:in `app'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/runner.rb:113:in `load_and_bind'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/cluster.rb:302:in `run'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/lib/puma/cli.rb:216:in `run'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/gems/puma-2.11.2/bin/puma:10:in `<top (required)>'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/bin/puma:23:in `load'
10:12:10 app.1        |     from /home/tom/.gem/ruby/2.2.1/bin/puma:23:in `<main>'
10:12:10 app.1        | exited with code 1
10:12:10 system       | sending SIGTERM to all processes