How to auto-install a gem's dependencies?

I have a gem to install an application /hello/ which is dependent on
another gem, which is on my server. What is the simplest way to makek my
gem automatically download and install that other gem?

This is the structure of my gem:
.
├── README
├── RELEASE
├── Rakefile
├── bin
│ └── hello
├── hello.gemspec
└── lib
└── hello
└── version.rb

The hello.gemspec contains:
spec.add_dependency(‘scriptingutils’,[">= 0.0.4"])

And scriptingutils-0.0.4.gem is on my server:
http://wybo.xs4all.nl/wdgems/
where the gem itself is in:
http://wybo.xs4all.nl/wdgems/gems/hello-0.1.gem