elixir: modify Elixir license to Apache 2.0

The current license is Eclipse Public license (epl10) which is
incorrect. I suspect this was intended to be Erlang Public License,
which was the license for OTP versions up to OTP 18. Since the minimum
OTP version for Elixir currently is 23, there should be no need to address
per-version license in this case.

pkgs/development/interpreters/elixir/generic-builder.nix

@@ -79,7 +79,7 @@ stdenv.mkDerivation ({
       with hot code upgrades.
     '';
 
-    license = licenses.epl10;
+    license = licenses.asl20;
     platforms = platforms.unix;
     maintainers = teams.beam.members;
   };