Reported by Alexander Blume at
<https://github.com/BIMSBbioinfo/guix.install/issues/4>.
* guix/import/cran.scm (format-inputs): Use UPSTREAM-INPUT-DOWNSTREAM-NAME
when %INPUT-STYLE is set to 'SPECIFICATION.
Change-Id: I2f0963af197896aafd613b253d8712e41a716e52