Fixed broken assets compilation.

Currently assets compilation is broken against following versions of rails and rails-tinymce (from the Gemfile.lock):

    rails (= 3.1.3)
    tinymce-rails (3.5.8.3)
    tinymce-rails-imageupload (3.5.8.5)  
    
Part of output of rake assets:precompile --trace:

** Execute assets:precompile:primary
rake aborted!
wrong number of arguments (2 for 3)
/home/oleg/workspace/ditto/web/shop/vendor/local/ruby/1.9.1/gems/tinymce-rails-3.5.8.3/lib/tinymce/rails/asset_installer.rb:6:in `initialize'
/home/oleg/workspace/ditto/web/shop/vendor/local/ruby/1.9.1/gems/tinymce-rails-imageupload-3.5.8.5/lib/tasks/tinymce-uploadimage-assets.rake:13:in `new'
/home/oleg/workspace/ditto/web/shop/vendor/local/ruby/1.9.1/gems/tinymce-rails-imageupload-3.5.8.5/lib/tasks/tinymce-uploadimage-assets.rake:13:in `block in <top (required)>'

This commit is fixing the problem.