Fix rubocop warnings

[nzwsch]

I recently made a comment urging the release of kredis.
Thank you for releasing 1.6.0.
I don't know if this is a result of that, but I noticed that the tests in the main branch are red.
Fortunately, I ran Rubocop locally and all errors were resolved.
I don't know if this qualifies as an open source contribution, but let me submit it as a PR.

Here is my output:

$ bundle exec rubocop
Inspecting 56 files
........................................................

56 files inspected, no offenses detected

[dhh]

I don't like any of those fixes. Should tell rubocop to ignore them instead.

[nzwsch]

We have two options.

The first is that this Rubocop rule references a rule in Rails itself, and Rails allows AssertPredicate, so we need to disable this one.
The second would be to add AssertPredicate to the .rubocop.yml file as an exception.

Which is preferred?

[dhh]

Let's adopt https://github.com/rails/rubocop-rails-omakase/.

[dhh]

Fixed in 01a893b.