rage: fix license for unstable

Beginning with the next development release (> 7.0.0.9)
Ragel is licensed under an MIT style license. Ragel 6
remains under GPL v2. Please see the file COPYING in the
source.

pkgs/development/tools/parsing/ragel/default.nix

···
 }:
 
 let
-  generic = { version, sha256 }:
+  generic = { version, sha256, license }:
     stdenv.mkDerivation rec {
       name = "ragel-${version}";
 
···
       meta = with stdenv.lib; {
         homepage = http://www.complang.org/ragel;
         description = "State machine compiler";
-        license = licenses.gpl2;
+        inherit license;
         platforms = platforms.unix;
         maintainers = with maintainers; [ pSub ];
       };
···
   ragelStable = generic {
     version = "6.10";
     sha256 = "0gvcsl62gh6sg73nwaxav4a5ja23zcnyxncdcdnqa2yjcpdnw5az";
+    license = stdenv.lib.licenses.gpl2;
   };
 
   ragelDev = generic {
     version = "7.0.0.10";
     sha256 = "1v4ddzxal4gf8l8nkn32qabba6nbpd2mg8sphgmdn8kaqv52nmj0";
+    license = stdenv.lib.licenses.mit;
   };
 }