Fix using add_resource with a block after gem in custom generators

[teknofire]

This fixes using add_source with a block after calling gem in a custom generator. Otherwise it tries to create a Gemfile with the output from both methods on the same line and would then throw an error when bundle install gets run

for example if a custom generator had the following

gem "font-awesome-rails"

add_source "https://rails-assets.org" do
  gem 'rails-assets-bootstrap'
  gem 'rails-assets-jasny-bootstrap'
end

it would generate

gem 'font-awesome-rails'source 'https://rails-assets.org' do
  gem 'rails-assets-bootstrap'
  gem 'rails-assets-jasny-bootstrap'
end

and now generates

gem 'font-awesome-rails'
source 'https://rails-assets.org' do
  gem 'rails-assets-bootstrap'
  gem 'rails-assets-jasny-bootstrap'
end

[rails-bot]

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @pixeltrix (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[senny]

Can you move that above the ## Rails 5.0.0.beta1 (December 18, 2015) ## line?

[senny]

@teknofire could you squash your commits?

[teknofire]

@senny Ok, that should take care of it although the tests fail on the something in the rails master

[senny]

@teknofire thank you 💛