Log Message:
gallery-dl: Update to 1.8.7

Changes:
1.8.7
-----
Additions:
 - Support for
   - `vanillarock` (#254)
   - `nsfwalbum`   (#287)
 - `artist` and `tags` metadata for `hentaicafe` (#238)
 - `description` metadata for `instagram` (#310)
 - Format string option to replace a substring with another
   - `R<old>/<new>/` (#318)

Changes:
 - Delete empty archives created by the `zip` post-processor (#316)

Fixes:
 - Handle `hitomi` Game CG galleries correctly (#321)
 - Miscellaneous fixes for `deviantart`, `hitomi`, `pururin`, `kissmanga`,
   `keenspot`, `mangoxo`, `imagefap`