As discourse. The console output you pasted says it nice and clearly, too:
Don't run Bundler as root.
Hmm, yeah, that’s never going to end well. Fixed the howto.
Unfortunately, chmod +x won’t work because the file doesn’t have a “shebang” (#!/usr/bin/ruby or similar) to tell the system what language it’s in. I’ve just changed the howto to run ruby explicitly; if you do that, it’ll work better (or at least break differently).