Log Message:
gallery-dl: Update to 1.8.1

Changes:
1.8.1
-----
### Added
 - Support for:
   - `35photo` (#162)
   - `500px` (#185)
 - `instagram` extractor for hashtags (#202)
 - Option to get more metadata on `deviantart` (#189)
 - Man pages and bash completion (#150)
 - Snap improvements (#197, #199, #207)
### Changed
 - Metadata for `luscious` albums
 - FFmpeg arguments for `--ugoira-conv`
### Fixed
 - `tumblr` avatar URLs when not using OAuth1.0 (#193)
 - `instagram` multi-image posts (#178, #201)
 - Miscellaneous issues on `exhentai`, `komikcast`