Warning:

Error: The brew link step did not complete successfully The formula built, but is not symlinked into /usr/local Could not symlink share/doc/node/gdbinit /usr/local/share/doc/node is not writable.

sudo chmod 776 /usr/local/lib
brew link --overwrite node
Outputs: Linking /usr/local/Cellar/node/9.6.1... 49 symlinks created
sudo chmod 755 /usr/local/lib