change md5sum to sha256sum for a few packages

pkgs/misc/beep/default.nix

@@ -7,7 +7,7 @@ stdenv.mkDerivation {
   name = "beep-1.3";
   src = fetchurl {
     url = http://www.johnath.com/beep/beep-1.3.tar.gz;
-    md5 = "49c340ceb95dbda3f97b2daafac7892a";
+    sha256 = "0bgch6jq5cahakk3kbr9549iysf2dik09afixxy5brbxk1xfzb2r";
   };
 
   makeFlags = "INSTALL_DIR=\${out}/bin/ MAN_DIR=\${out}/man/man1/";

pkgs/misc/cups/default.nix

@@ -10,7 +10,7 @@ stdenv.mkDerivation {
 
   src = fetchurl {
     url = "http://ftp.easysw.com/pub/cups/${version}/cups-${version}-source.tar.bz2";
-    md5 = "de3006e5cf1ee78a9c6145ce62c4e982";
+    sha256 = "07xq6rwpg2r6vjvimd53f259ijx50cnw3p7s1sk84z4dddi6vnfk";
   };
 
   buildInputs = [ pkgconfig zlib libjpeg libpng libtiff libusb ]

pkgs/misc/emulators/atari800/default.nix

@@ -9,7 +9,7 @@ stdenv.mkDerivation {
   };
   rom = fetchurl {
     url = mirror://sourceforge/atari800/xf25.zip;
-    md5 = "4dc3b6b4313e9596c4d474785a37b94d";
+    sha256 = "12jbawxs04i0wm3910n7f3phsybdp8nndxc0xlsnzp8k0k8hmblq";
   };
   buildInputs = [unzip zlib SDL];
   configureFlags = "--target=sdl";

pkgs/misc/screensavers/rss-glx/default.nix

@@ -5,7 +5,7 @@ stdenv.mkDerivation {
   
   src = fetchurl {
     url = mirror://sourceforge/rss-glx/rss-glx_0.8.1.tar.bz2;
-    md5 = "a2bdf0e10ee4e89c8975f313c5c0ba6f";
+    sha256 = "1fs2xavyf9i6vcdmdnpyi9rbnrg05ldd49bvlcwpn5igv2g400yg";
   };
 
   buildInputs = [x11 mesa pkgconfig imagemagick libtiff bzip2];