Changing bower package cache directory

bower caches packages in ~/.cache/bower. How can I change the directory? bower's document says "Add the following in .bowerrc" but it's totally wrong.

"storage": {
  "cache" : "~/.bower/cache",
  "registry" : "~/.bower/registry"
}

I try the configuration and run bower install but nothing changed. I finally found out correct configuration in bower/config repo.

"storage": {
  packages: ".bower/packages",
  registry: ".bower/registry"
}

Why the document of famous software such as bower is wrong?

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