curl: fetchurl more securely

pkgs/tools/networking/curl/default.nix

···
   name = "curl-7.58.0";
 
   src = fetchurl {
-    url = "http://curl.haxx.se/download/${name}.tar.bz2";
+    url = "https://curl.haxx.se/download/${name}.tar.bz2";
     sha256 = "0cg7klhf1ksnbw5wvwa802qir877zv4y3dj7swz1xh07g3wq3c0w";
   };