macOS10.9.5でhomebrew をインストール。
ターミナルで
①brew install nodeを実行すると
→「node-0.12.4 already installed, it's just not linked」（リンクが張られてない）
②brew link nodeでリンクを張ろうとすると
→Linking /usr/local/Cellar/node/0.12.4...
Error: Could not symlink include/node/android-ifaddrs.h
/usr/local/include/node is not writable.
権限がない？とでます。
この時点でbrew doctorを実行すると
Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry and just ignore them. Thanks!
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
brew link nodeをしなさい。ということで②に戻ってしまいます。
どうすればよいのでしょうか