Fix tests for compatibility with redis-rb v5.0

[mishina2228]

This PR fixes failing tests with redis-rb v5.0,
and also added matrix for redis-rb v4 and v5.

Here are the details:

• Field and value for hash must be String, Integer or Float
  • redis-rb 4.x used to call to_s on arguments, but redis-rb 5.x won't.
  • See here: Unsupported command argument type: EtOrbi::EoTime redis/redis-rb#1143 (comment)
• Use Resque::DataStore#reconnect instead of removed Redis::Client#reconnect
  • Use Resque::DataStore#reconnect for redis-rb v5.0 #756 already has this change,
    but I would like to make all CI pass, so I included the same one.
• Added matrix redis version
  • Test with redis-rb v4.x and v5.x
  • Update resque test matrix from ~> 2.2.0 to ~> 2.4.0
  • Exclude the combination of the following:
    • redis-rb v5.x with Ruby 2.4 or older
    • redis-rb v5.x with Resque 1.27.x
  • Fix resque-version in exclusions
    • They should be started with ~> .

[mishina2228]

As stated at #753 (comment), some of the tests seem flaky. I will look into this a bit.

[mishina2228]

OK, I found the cause of the problem.
It seems that the tests fail if data from the previous test case is still in Redis.
I made sure that flushall is executed like other test files.

[PatrickTulskie]

Having some CI/branch protection issues. Lemme get that sorted out with @iloveitaly and then I can get this into master and a new release out.