rkt: bump to 1.24.0

[dongsupark]

As rkt 1.24.0 supports an experimental attach command, minikube iso image should also contain the new version.

See also rkt/rkt#3396 (comment)
/cc @s-urbaniak

[dongsupark]

I've also tested with "make minikube_iso". rkt 1.24 gets included in the iso image.

[s-urbaniak]

LGTM, thanks!

Note that rkt attach is not integrated in k8s itself at this point.

[codecov-io]

Codecov Report

Merging #1128 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1128   +/-   ##
=======================================
  Coverage   31.59%   31.59%           
=======================================
  Files          45       45           
  Lines        2114     2114           
=======================================
  Hits          668      668           
  Misses       1314     1314           
  Partials      132      132

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[r2d4]

LGTM thanks for upgrading this!