Fix test on ruby-2.4-x64
Fix test on ruby-2.4-x64

The tests expect to switch to a different ruby version than the
currently running version. So remove the static ruby version
and look for a alternative version from a list.

larskanis/rubyinstaller2,larskanis/rubyinstaller2,oneclick/rubyinstaller2,oneclick/rubyinstaller2,larskanis/rubyinstaller2,oneclick/rubyinstaller2