Log Message:
gallery-dl: Update to 1.8.3

Changes:
1.8.3
-----
### Additions
- Support for
  - `plurk` (#212)
  - `sexcom` (#147)
- `--clear-cache`
- `date` metadata fields for `deviantart`, `twitter`, and `tumblr` (#224, #232)

### Changes
- Standalone executables are now built using PyInstaller:
  - uses the latest CPython interpreter (Python 3.7.3)
  - available on several platforms (Windows, Linux, macOS)
  - includes the `certifi` CA bundle, `youtube-dl`, and `pyOpenSSL` on Windows

### Fixes
- Patch `urllib3`'s  default list of SSL/TLS ciphers to prevent Cloudflare
  CAPTCHAs (#227)
  - Windows users need to install `pyOpenSSL` for this to take effect
- Provide fallback URLs for `twitter` images (#237)
- Send `Referer` headers when downloading from `hitomi` (#239)
- Updated login procedure on `mangoxo`