bundle install --deployment fails with new source blocks

I'm getting bit by this bug when trying to use source blocks for private gems. Install, update, install --local all work fine, but install --deployment throws:

```
$ b install --deployment --local
You are trying to install in deployment mode after changing
your Gemfile. Run `bundle install` elsewhere and add the
updated Gemfile.lock to version control.

You have added to the Gemfile:
* source: rubygems repository https://user:pass@a-private-gem.server/
* source: rubygems repository https://rubygems.org/

You have deleted from the Gemfile:
* source: rubygems repository https://user:pass@a-private-gem.server/,
https://rubygems.org/

You have changed in the Gemfile:
* a-private-gem from `rubygems repository https://user:pass@a-private-gem.server/` to `no
specified source`
```