resolve ruby versions symlinks when applying to the env

This ensures that an actual version path (not a symlinked path)
is always used in the ENV vars.  This means that symlinking ruby
versions will have no effect on the path related ENV vars.  The
symlinks will only be used for referencing versions.

This is good b/c it normalizes things.  Plus you can safely treat
symlinks are references only.  There may be future PRs that add some
behavior related to this - not sure yet.