How to fix npm to find correct node enviorment?
I consider this a workaround, if there is a way to get node upgraded the brew way, I appreciate it.

It seems that boxen in its standard configuration only provides v0.10.21 yet once npm updated itself, it expects v0.10.26.

I tried to reconfigure boxen to install node yet failed.

I then went along and installed NodeJs manually over the pgk provided by nodejs.org and globally installed node 0.10.26. Then nodenv was able to find that version and by setting 

nodenv global v0.10.26


npm started working again. I then had to reinstall certain packages not expecting that v0.10.26 version, e.g. bower version.