Log Message:
gallery-dl: Update to 1.8.4

Changes:
### Additions
 - Support for
   - `patreon` (#226)
   - `hentainexus` (#256)
 - `date` metadata fields for `pixiv` (#248), `instagram` (#250),
   `exhentai`, and `newgrounds`
### Changes
 - Improved `flickr` metadata and video extraction (#246)
### Fixes
 - Download original GIF animations from `deviantart` (#242)
 - Ignore missing `edge_media_to_comment` fields on `instagram` (#250)
 - Fix serialization of `datetime` objects for `--write-metadata` (#251, #252)
 - Allow multiple post-processor command-line options at once (#253)
 - Prevent crash on `booru` sites when no tags are available (#259)
 - Fix extraction on `instagram` after `rhx_gis` field removal (#266)
 - Avoid Cloudflare CAPTCHAs for Python interpreters built
   against OpenSSL < 1.1.1
 - Miscellaneous fixes for `luscious`