How to set the other template engine (Tenjin) as the default in Rails ()instead of Erubis)?

The problem I want to solve is that Erubis (the default Rails template
engine) parses html unprofessionally - there are many blank lines and
space characters are left in the result page. -%> (minuses in tags) do
not help.

I do not want to switch Haml or Slim because I prefer plain html.

I want to try out Tenjin
(http://www.kuwata-lab.com/tenjin/rbtenjin-users-guide.html) but do not
know how to make it to be the default template engine.

By Rails guide it is done like this:

config.generators do |g|
  g.template_engine(:tenjin)
end

But it doesn't work. I get an error:

# in my Gemfile
gem("tenjin")

# now generate
C:\ruby\Sites\Test>rails generate controller test
      create app/controllers/test_controller.rb
       error tenjin [not found] # NOT FOUND
      invoke test_unit
      create test/functional/test_controller_test.rb
      invoke helper
      create app/helpers/test_helper.rb
      invoke test_unit
      create test/unit/helpers/test_helper_test.rb
      invoke assets
      invoke js
      create app/assets/javascripts/test.js
      invoke scss
      create app/assets/stylesheets/test.css.scss

How to turn off the default erubis and turn on Tenjin?

Or if there is some magic how to turn off blank spaces of Erubis, it is
even better.