Bump manageiq-style for rexml CVEs

[Fryguy]

@kbrock Please review. This should remove some of the Mend Bolt issues around rexml CVEs.

[Fryguy]

Dropping old Ruby versions in #172

[kbrock]

sigh...

Maybe require different rubocop versions for different versions of ruby?
Or maybe drop ruby < 2.7. Locally anything older than 2.7 is too hard to wrangle gems into supporting.

    manageiq-style (>= 1.5.3) was resolved to 1.5.3, which depends on
      rubocop (= 1.56.3) was resolved to 1.56.3, which depends on
        Ruby (>= 2.7.0)

  Current Ruby version:
    Ruby (= 2.4.10)
Error: The process '/opt/hostedtoolcache/Ruby/2.4.10/x64/bin/bundle' failed with exit code 6

[kbrock]

@Fryguy please rebase

[Fryguy]

@kbrock Done.