graphics/imv: update to 3.1.0

From ChangeLog (https://github.com/eXeC64/imv/blob/master/CHANGELOG):

• Added support for multiple image loaders, allowing imv to use libraries other than FreeImage. This adds support for SVGs, and in the future, other formats as required.
• Loaders added for libpng, libtiff, librsvg, libturbojpeg.
• Added support for binding multiple commands to a single key
• Support for hidpi rendering with SDL >= 2.0.10
• Added -v flag to show version number
• Allow 'Escape' to be bound, changing bind abort sequence to 2x'Escape'
• Fixed bug where path list from stdin would sometime be truncated
• New releases only published under the MIT license, with FreeImage optionally used under the FIPL
• Fixed several memory leaks
• Miscellaneous code cleanup and documentation fixes

While here, pet portlint.

Reported by: portscout