Ainda não entendo por que , mas preciso executar npm install -g npm
duas vezes para que tenha o efeito desejado:
vagrant@box:~$ npm -v
1.3.10
vagrant@box:~$ sudo npm install -g npm
npm http GET https://registry.npmjs.org/npm
npm http 200 https://registry.npmjs.org/npm
npm http GET https://registry.npmjs.org/npm/-/npm-2.1.12.tgz
npm http 200 https://registry.npmjs.org/npm/-/npm-2.1.12.tgz
/usr/local/bin/npm -> /usr/local/lib/node_modules/npm/bin/npm-cli.js
[email protected] /usr/local/lib/node_modules/npm
vagrant@box:~$ npm -v
1.3.10
vagrant@box:~$ sudo npm install -g npm
/usr/bin/npm -> /usr/lib/node_modules/npm/bin/npm-cli.js
[email protected] /usr/lib/node_modules/npm
vagrant@box:~$ npm -v
2.1.12