metaBuildEnv: use sha256 hash

pkgs/development/compilers/meta-environment/meta-build-env/default.nix

···
   name = "meta-build-env-0.1";
   src = fetchurl {
     url = http://www.meta-environment.org/releases/meta-build-env-0.1.tar.gz ;
-    md5 = "827b54ace4e2d3c8e7605ea149b34293";
+    sha256 = "1imn1gaan4fv73v8w3k3lgyjzkcn7bdp69k6hlz0vqdg17ysd1x3";
   };
 
   meta = {