fix boot on 1.9.3-p385

  rails-2.3.14.github14/lib/initializer.rb:906:in `replace': can't modify frozen String (RuntimeError)
  from gems/rails-2.3.14.github14/lib/initializer.rb:906:in `set_root_path!'
  from gems/rails-2.3.14.github14/lib/initializer.rb:860:in `initialize'
  from gems/rails-2.3.14.github14/lib/initializer.rb:110:in `new'
  from gems/rails-2.3.14.github14/lib/initializer.rb:110:in `run'
  from github/config/environment.rb:22:in `<top (required)>'