Log Message:
gallery-dl: Update to 1.8.6

Changes:
1.8.6
-----
### Additions
 - Support for
   - `slickpic` (#249)
   - `xhamster` (#281)
   - `pornhub`  (#282)
   - `8muses`   (#305)
 - `extra` option for `deviantart` to download Sta.sh content linked in
   description texts (#302)
### Changes
 - Detect `directlink` URLs with upper case filename extensions (#296)
### Fixes
 - Improved error handling for `tumblr` API calls (#297)
 - Fixed extraction of `livedoor` blogs (#301)
 - Fixed extraction of special `deviantart` Sta.sh items (#307)
 - Fixed pagination for specific `keenspot` comics