Bump version to v2.26.0

[bquorning]

I think it’s time for the first release of the year. Changes:

• Add new RSpec/RedundantPredicateMatcher cop. (@ydah)
• Add new RSpec/RemoveConst cop. (@swelther)
• Add support for correcting "it will" (future tense) for RSpec/ExampleWording. (@jdufresne)
• Add support for symbol style for RSpec/SharedExamples. (@jessieay)
• Ensure PendingWithoutReason can detect violations inside shared groups. (@robinaugh)

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[bquorning]

Maybe we can still add #1722 to this release?

[ydah]

Maybe we can still add #1722 to this release?

IMO we can still add. @pirj what do you think?

[bquorning]

I left a few comments on #1722.

[pirj]

No objections to #1722

[bquorning]

We’ll put #1722 in the next release.