fetchzip and friends: Set "name" to "source" by default

This makes them produce the same store paths as builtins.fetchgit,
builtins.fetchTarball etc. See
https://github.com/NixOS/nix/commit/65b5f177b5fbb1b0778ede047a13a3cee9c59cfe.

pkgs/build-support/fetchzip/default.nix

@@ -11,10 +11,11 @@
   stripRoot ? true
 , url
 , extraPostFetch ? ""
+, name ? "source"
 , ... } @ args:
 
 lib.overrideDerivation (fetchurl ({
-  name = args.name or (baseNameOf url);
+  inherit name;
 
   recursiveHash = true;