Error on keybase update

keybase update
info: Computed npm install prefix: /usr/local
info: Found keybase-installer: keybase-installer v1.0.1
info: Using default npm install prefix
info: Attempting software upgrade.....
info: Running `keybase-installer -g gpg2`
info: Made temporary directory: /var/folders/zv/_g0_flts34l_twwll2x449pw0000gn/T/keybase_install_7AoAaWVyW6CDVv7mv82wkg
info: Using keyset version v1
info: Fetching URL https://dist.keybase.io/sig/files/1/index.asc
info: Fetching URL https://dist.keybase.io/pkg/stable
info: Fetching URL https://dist.keybase.io/sig/files/1/keybase-0.8.20.tgz.asc
info: verified signature of keybase-0.8.20.tgz against keybase-0.8.20.tgz.asc
info: Running npm install keybase-0.8.20.tgz: this may take a minute, please be patient
npm ERR! Darwin 14.4.0
npm ERR! argv "node" "/usr/local/bin/npm" "install" "-g" "/var/folders/zv/_g0_flts34l_twwll2x449pw0000gn/T/keybase_install_7AoAaWVyW6CDVv7mv82wkg/keybase-0.8.20.tgz"
npm ERR! node v0.12.7
npm ERR! npm  v2.13.4
npm ERR! path /usr/local/bin/keybase
npm ERR! code EACCES
npm ERR! errno -13

npm ERR! Error: EACCES, unlink '/usr/local/bin/keybase'
npm ERR!     at Error (native)
npm ERR!  { [Error: EACCES, unlink '/usr/local/bin/keybase'] errno: -13, code: 'EACCES', path: '/usr/local/bin/keybase' }
npm ERR!
npm ERR! Please try running this command again as root/Administrator.
npm ERR! error rolling back Error: EACCES, unlink '/usr/local/bin/keybase'
npm ERR! error rolling back     at Error (native)
npm ERR! error rolling back  { [Error: EACCES, unlink '/usr/local/bin/keybase'] errno: -13, code: 'EACCES', path: '/usr/local/bin/keybase' }

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/mac/Dropbox/projects/tmp/learngit/npm-debug.log
info: cleaning up tmpdir /var/folders/zv/_g0_flts34l_twwll2x449pw0000gn/T/keybase_install_7AoAaWVyW6CDVv7mv82wkg
error: exit code 243
error: exit code 254

Start by reproducing keybase update on the reported Darwin setup and inspect the npm install -g step targeting /usr/local/bin/keybase. Compare the command's permissions and rollback behavior; done means the update completes without the EACCES unlink failure or clearly reports the required action.