Add always_braces to Style/BlockDelimiters

[iGEL]

This style always prefers braces over do...end.

This style always prefers braces over do...end. Similar to double quotes, some developers don't want to bother with changing the style when adding or removing a line or debate, whether a blocks like

date = Timecop.freeze(1.year.ago) { format_date(Time.now) }
customer = Timecop.freeze(1.year.ago) { create(:customer) }

are functional or procedual.

I didn't add a always_do_end style, as I don't think that someone wants to enforce this in all situation (chaining, ...).

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[bbatsov]

Thanks!