Disable TLS verification for builtin fetchurl

This makes it consistent with the Nixpkgs fetchurl and makes it work
in chroots. We don't need verification because the hash of the result
is checked anyway.

src/nix-prefetch-url/nix-prefetch-url.cc

@@ -158,7 +158,7 @@ int main(int argc, char * * argv)
             auto actualUri = resolveMirrorUri(state, uri);
 
             /* Download the file. */
-            auto result = downloadFile(actualUri);
+            auto result = downloadFile(actualUri, DownloadOptions());
 
             AutoDelete tmpDir(createTempDir(), true);
             Path tmpFile = (Path) tmpDir + "/tmp";