sic: fix empty $out

Make needs () around variable names, or it'll interpret $out as $o followed by `ut`

pkgs/applications/networking/irc/sic/default.nix

···
   name = "sic-${version}";
   version = "1.2";
 
-  makeFlags = "PREFIX=$out";
+  makeFlags = "PREFIX=$(out)";
   src = fetchurl {
     url = "http://dl.suckless.org/tools/sic-${version}.tar.gz";
     sha256 = "ac07f905995e13ba2c43912d7a035fbbe78a628d7ba1c256f4ca1372fb565185";