Add tip about using RDoc's --pipe command to quickly test the output of
a piece of documentation.

This can be useful for trying out combinations of markup and code, as
discussed in rails/rails@225bcad
Fix coffeescript sample [ci skip]

Replace bind() with on() as suggested by the JQuery bind() documentation: https://api.jquery.com/bind/
Add hint to error message of task db:migrate:down
rm delegate methods that are not actually used
:scissors: whitespace
remove more delegate methods
Getting started guide fixes & Explain X-SendFile a little better, with links

Explain how form_for :article is able to pull in the properties of @article
Make it clear that article_id is generated due to the association set up

Add link to the rails function that uses X-Sendfile.
Add links to apache and nginx docs for the header
remove unused fixtures from sqlite3 test cases
fix guide active_support_core_extensions. add Note to String#indent [ci skip]
updated Travis build status image url
Merge pull request #14058 from lantoli/master

updated Travis build status image url
Merge pull request #14059 from tbpgr/guides_active_support_core_ext

[Guides] fix guide active_support_core_extensions. add Note to String#indent [ci skip]
Merge pull request #14057 from rajcybage/Ar_remove_unnecessary_fixtures

Remove unused fixtures from sqlite3 test case
Merge pull request #14048 from pcreux/better-error-message-db-migrate-down

Add hint to error message of task db:migrate:down
fix path shown in mailer's templates
Merge pull request #14060 from kassio/master

Fix path shown in mailer's templates
Add verb to sanitization note
Merge pull request #14061 from davejachimiak/add_verb_in_guides

Add verb to sanitization note
remove scope_chain delegate
remove chain delegate