Added slim layout file and removed erb layout file

app_template.rb

### Rails app generator template. Run it:
### rails new _app_name_ -m https://gist.githubusercontent.com/DamirSvrtan/28a28e50d639b9445bbc/raw/app_template.rb

bin_setup_file = <<-FILE
#!/bin/sh
bundle install
bundle exec rake db:setup
FILE

File.open('bin/setup', 'w'){|file| file.write(bin_setup_file)}

remove_file "README.rdoc"
create_file "README.md", "Development: run ./bin/setup"
run 'mv app/assets/stylesheets/application.css app/assets/stylesheets/application.scss'

database_type = ask("Do you want to use postgres or mysql?", limited_to: ["pg", "mysql"])

adapter = if database_type == 'pg'
  gem 'pg'
  'postgresql'
else
  gem 'mysql2'
  'mysql2'
end

database_file = <<-FILE
default: &default
  adapter: <%= adapter %>
  pool: 5
  timeout: 5000
  host: localhost
  username: root

development:
  <<: *default
  database: <%= @app_name %>_development
  password:

test:
  <<: *default
  database: <%= @app_name %>_test

production:
  <<: *default
  database: <%= @app_name %>_production
FILE

File.open('config/database.yml', 'w') do |file|
  file.write(ERB.new(database_file).result(binding))
end

# Remove unwanted gems. spring will be added later in the development group of gems
%w(spring coffee-rails sqlite3).each do |unwanted_gem|
  gsub_file("Gemfile", /gem '#{unwanted_gem}'.*\n/, '')
end

# Replace erb layout file with slim layout file
layout_file = <<-FILE
doctype html
html
  head
    title Site title

    = stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track' => true
    = javascript_include_tag 'application', 'data-turbolinks-track' => true
    = csrf_meta_tags

  body
    = yield
FILE

File.delete('app/views/layouts/application.html.erb')
File.open('app/views/layouts/application.html.slim', 'w') do |file|
  file.write(ERB.new(layout_file).result(binding))
end 

# remove commented lines
gsub_file("Gemfile", /#.*\n/, '')
# remove double newlines
gsub_file("Gemfile", /^\n\n/, '')

simple_form_installation = "simple_form:install"

if yes?('Use bootstrap?')
  gem 'bootstrap-sass'
  simple_form_installation << " --bootstrap"
end

gem 'simple_form'
gem 'slim-rails'
gem 'draper'

gem_group :development do
  gem 'spring'
  gem 'better_errors'
  gem 'binding_of_caller'
  gem 'quiet_assets'
  gem 'pry-rails'
  gem 'bullet'
  gem 'traceroute'
  gem 'letter_opener'
end

run "bundle install"

generate simple_form_installation

git :init
%w(.sass-cache powder public/system dump.rdb logfile .DS_Store).each do |gitignored|
  append_file ".gitignore", gitignored
end
git add: ".", commit: "-m 'Initial commit'"

I agree completely. :)