Do you want to request a feature or report a bug?

Feature.

What is the current behavior?
yarn upgrade ignores indirect dependencies, so users can't upgrade them in yarn.lock. If I missed something, please tell me.

If the current behavior is a bug, please provide the steps to reproduce.

• Suppose a new empty project, run yarn add is-alphanumerical@1.0.0
  • 2 indirect dependencies, is-alphabetical and is-decimal, will be installed and saved in yarn.lock
  • the latest version of is-alphabetical is 1.0.1 now, if another new version, say 1.0.2 was released(to test, you can release 2 test packages by yourself or modify is-alphabetical to be 1.0.0 in yarn.lock, ** I know modifying yarn.lock directly is not a regular operation**)
• No matter which of following ways, yarn always says All of your dependencies are up to date
  • yarn upgrade is-alphabetical
  • yarn upgrade-interactive
  • yarn upgrade-interactive is-alphabetical

What is the expected behavior?
yarn upgrade also supports indirect dependencies.

Please mention your node.js, yarn and operating system version.
Node 8.9.0
yarn 1.3.2
OSX 10.12.6