homebrewアップデート

$ brew doctor
Warning: The system curl on 10.8 and below is often incapable of supporting
modern secure connections & will fail on fetching formulae.

We recommend you:
  brew install curl

Warning: You have unlinked kegs in your Cellar
Leaving kegs unlinked can lead to build-trouble and cause brews that depend on
those kegs to fail to run properly once built. Run `brew link` on these:
  node

Warning: You are using macOS 10.8.
We (and Apple) do not provide support for this old version.
You may encounter build failures or other breakages.
Please create pull-requests instead of filing issues.

$ brew link node`

$ brew update