[DRE-maint] diaspora post-install error

[Vito Caputo]

I just tried setting up a diaspora instance in a fresh i686 debian sid
debootstrap booted under nspawn, post-install fails unexpectedly with:

Setting up diaspora (0.7.9.0+dfsg-4) ...
Could not find gem 'rubyzip (>= 1.2.2, ~> 1.2)' in any of the gem sources listed in your Gemfile.
dpkg: error processing package diaspora (--configure):
 installed diaspora package post-installation script subprocess returned error exit status 1