Correct Nix flake licensing & add ISC License

woo, removal of miniLZO means no more GPLv3+!

(All contributors signed off on this relicense.)

LICENSE.txt

@@ -0,0 +1,15 @@
+ISC License
+
+Copyright (c) 2020-2021 water111
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

flake.nix

@@ -118,7 +118,7 @@
           meta = with lib; {
             description = "OpenGOAL port of Naughty Dog's GOAL";
             homepage = "https://github.com/water111/jak-project";
-            license = lib.licenses.gpl3Plus;
+            license = lib.licenses.isc;
             maintainers = with maintainers; [ bb010g ];
             platforms = platforms.all;
           };