farbfeld: 2 -> 3 and use correct license (isc)

pkgs/development/libraries/farbfeld/default.nix

···
 
 stdenv.mkDerivation rec {
   name = "farbfeld-${version}";
-  version = "2";
+  version = "3";
 
   src = fetchgit {
     url = "http://git.suckless.org/farbfeld";
     rev = "refs/tags/${version}";
-    sha256 = "1rj6pqn50v6r7l3j7m872fgynxsh22zx863jg0jzmb4x6wx2m2qv";
+    sha256 = "1k9cnw2zk9ywcn4hibf7wgi4czwyxhgjdmia6ghpw3wcz8vi71xl";
   };
 
   buildInputs = [ libpng libjpeg ];
···
 
   meta = with stdenv.lib; {
     description = "Suckless image format with conversion tools";
-    license = licenses.mit;
+    license = licenses.isc;
     platforms = platforms.linux;
     maintainers = with maintainers; [ pSub ];
   };