So if you get this message, while doing bundle install:

/ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/spec_set.rb:92:in `block in materialize':
Could not find minitest-4.7.5 in any of the sources (Bundler::GemNotFound)
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/spec_set.rb:85:in `map!'
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/spec_set.rb:85:in `materialize'
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/definition.rb:114:in `specs'
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/definition.rb:159:in `specs_for'
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/definition.rb:148:in `requested_specs'
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/environment.rb:18:in `requested_specs'
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler/runtime.rb:13:in `setup'
from /ruby/gems/2.1.0-p0/gems/bundler-1.5.0/lib/bundler.rb:120:in `setup'
from /ruby/gems/2.1.0-p0/gems/rubygems-bundler-1.5.0/lib/rubygems-bundler/noexec.rb:74:in `setup'
from /ruby/gems/2.1.0-p0/gems/rubygems-bundler-1.5.0/lib/rubygems-bundler/noexec.rb:103:in `check'
from /ruby/gems/2.1.0-p0/gems/rubygems-bundler-1.5.0/lib/rubygems-bundler/noexec.rb:109:in `<top (required)>'
from /ruby/2.1.0-p0/rubygems/core_ext/kernel_require.rb:110:in `require'
from /ruby/2.1.0-p0/rubygems/core_ext/kernel_require.rb:110:in `rescue in require'
from /ruby/2.1.0-p0/rubygems/core_ext/kernel_require.rb:35:in `require'
from /ruby/gems/2.1.0-p0/gems/rubygems-bundler-1.5.0/lib/rubygems_executable_plugin.rb:4:in `block in <top (required)>'
from /ruby/gems/2.1.0-p0/gems/executable-hooks-1.2.4/lib/executable-hooks/hooks.rb:50:in `call'
from /ruby/gems/2.1.0-p0/gems/executable-hooks-1.2.4/lib/executable-hooks/hooks.rb:50:in `block in run'
from /ruby/gems/2.1.0-p0/gems/executable-hooks-1.2.4/lib/executable-hooks/hooks.rb:49:in `each'
from /ruby/gems/2.1.0-p0/gems/executable-hooks-1.2.4/lib/executable-hooks/hooks.rb:49:in `run'
from /Users/smithy/.rbenv/versions/2.1.0-p0-p247/bin/ruby_executable_hooks:10:in `<main>'

You need to update your bundler:

gem update bundler
Updating installed gems
Updating bundler
Fetching: bundler-1.5.2.gem (100%)
Successfully installed bundler-1.5.2
Parsing documentation for bundler-1.5.2
Installing ri documentation for bundler-1.5.2
Installing darkfish documentation for bundler-1.5.2
Gems updated: bundler