Remove deprecated `::File.exists?` Using `::File.exist?` instead.

Also fixed bug with symlinks what was checked the using `exists?` and `exist?` at same time, but in specs was mocked only `exists?`
@lamont-granquist did you checked the the rspec file what I mentioned?
`
when the target is a regular old file
    and the source does not exist
      should set the symlink target
      should update the current source of the existing link with an empty string
      should not set the owner (FAILED - 1)
      should not set the group (FAILED - 2)
    and the source exists
      should set the symlink target
      should update the current source of the existing link with an empty string
      should not set the owner (FAILED - 3)
      should not set the group (FAILED - 4)
    and is hardlinked to the source
      should set the symlink target
      should set the link type
      should update the source of the existing link to the link's target
      should not set the owner (FAILED - 5)
      should not set the group (FAILED - 6)
      when the desired state is identical
        create does no work
`
So as I understand FAILED specs not checking real behavior? Or what?

IN any case this logic is unclear. It must be working as expected in rspec file or rspec file is broken?