apacheHttpd: use sha256 hash instead of sha1

pkgs/servers/http/apache-httpd/2.4.nix

···
 
   src = fetchurl {
     url = "mirror://apache/httpd/httpd-${version}.tar.bz2";
-    sha1 = "gx7cqkx8j1kaaw6vb8j9nl2amhsbw0ai";
+    sha256 = "0n2yx3gjlpr4kgqx845fj6amnmg25r2l6a7rzab5hxnpmar985hc";
   };
 
   # FIXME: -dev depends on -doc