Bundler is rather slow at installing new/updated gems when someone else has committed changes to the Gemfile.lock. I decided to find a quicker way. I think this is quicker, it gives me progress output so it feels quicker anyway.
$ bundle check | egrep "[a-zA-Z0-9_-]+ \([0-9.]+\)" | sed -Ee \
's/^.* ([a-zA-Z0-9_-]+) \(([0-9.]+)\).*$/\1 -v="\2"/' | xargs -L1 gem install
Fetching: SystemTimer-1.2.3.gem (100%)
Building native extensions. This could take a while...
Successfully installed SystemTimer-1.2.3
1 gem installed
Fetching: net-ssh-2.1.4.gem (100%)
Successfully installed net-ssh-2.1.4
1 gem installed
Fetching: capistrano-2.5.21.gem (100%)
Successfully installed capistrano-2.5.21
1 gem installed
Fetching: ffi-1.0.7.gem (100%)
Building native extensions. This could take a while...
Successfully installed ffi-1.0.7
1 gem installed
Fetching: childprocess-0.1.8.gem (100%)
Successfully installed childprocess-0.1.8
1 gem installed
Fetching: selenium-webdriver-0.1.4.gem (100%)
Successfully installed selenium-webdriver-0.1.4
1 gem installed
Fetching: curb-0.7.15.gem (100%)
Building native extensions. This could take a while...
Successfully installed curb-0.7.15
1 gem installed
Fetching: daemons-1.1.2.gem (100%)
Successfully installed daemons-1.1.2
1 gem installed
Fetching: httparty-0.7.6.gem (100%)
When you HTTParty, you must party hard!
Successfully installed httparty-0.7.6
1 gem installed
Fetching: kgio-2.3.3.gem (100%)
Building native extensions. This could take a while...
Successfully installed kgio-2.3.3
1 gem installed
Fetching: resque-pool-0.2.0.gem (100%)
Successfully installed resque-pool-0.2.0
1 gem installed
Fetching: rspec-1.3.2.gem (100%)
Successfully installed rspec-1.3.2
1 gem installed
Fetching: rspec-rails-1.3.4.gem (100%)
Successfully installed rspec-rails-1.3.4
1 gem installed
Fetching: unicorn-3.5.0.gem (100%)
Building native extensions. This could take a while...
Successfully installed unicorn-3.5.0
1 gem installed
$ bundle check
The Gemfile's dependencies are satisfied