Refactor determination of max updated timestamp

`[].max # => nil`
[ci skip] Correct output and use valid options of number helpers
Remove deprecated method ActiveRecord::Base.quoted_locking_column
Merge pull request #15611 from akshay-vishnoi/doc_changes

[ci skip] Correct output and use valid options of number helpers
[ci skip] Add Docs for strip_insignificant_zeros option in number helpers
Merge pull request #15612 from akshay-vishnoi/delete-deprecated-method

Remove deprecated method ActiveRecord::Base.quoted_locking_column
[ci skip] Improve enable_starttls_auto documentation.
fix error with long keys in ActiveSupport::Cache::FileStore
Merge pull request #15614 from akshay-vishnoi/doc_changes

[ci skip] Add Docs for strip_insignificant_zeros option in number_to_human
Merge pull request #15615 from JuanitoFatas/doc/action-mailer

[ci skip] Improve enable_starttls_auto documentation (Action Mailer).
Merge pull request #15616 from apanzerj/fix_long_key_paths

fix error with long keys in ActiveSupport::Cache::FileStore
remove deprecation call while initializing `ClassCache` object
Merge pull request #15617 from kuldeepaggarwal/remove-deprecate-method

remove deprecation call while initializing `ClassCache` object
[ci skip] Refine Action Mailer guide.
* Wrap 80 words if possible.
* Make attachment hash options more readable. (L239-L243)

  Before:

  ![screenshot 2014-06-11 02 59 54](https://cloud.githubusercontent.com/assets/1000669/3235432/a91d0464-f0d2-11e3-9e4a-6af2b2a83f1a.png)

   After:

  ![screenshot 2014-06-11 02 59 36](https://cloud.githubusercontent.com/assets/1000669/3235428/a47b28dc-f0d2-11e3-806c-cfaedd3f15df.png)

* L619 Wrap "location" in code: `"location"`.
* L628 Use actual section name.
* L697 Remove unnecessary `./` when refer to other guide.
Merge pull request #15618 from JuanitoFatas/doc/action-mailer-guide

[ci skip] Refine Action Mailer guide.
[ci skip] Fix doc for javascript_helper
Correct Bundler link [ci skip]
Merge pull request #15620 from aditya-kapoor/correct-bundler-link

Correct Bundler link [ci skip]
No need to decorate columns twice

We never want result types to override column types, and
`decorate_columns` can only affect column types. No need to go through
the decoration multiple times, we can just exclude the column types from
the result types instead.
Merge pull request #15619 from aditya-kapoor/fix-js-doc

[ci skip] Fix doc for javascript_helper