Installing gem: how to let it look in the Gemfile for dependencies?

ruby-talk
1

I have a gem, which depends on an other gem, which is on my server.
So, the gem is like:

  #!/usr/bin/env ruby
  gem 'scriptingutils', '>= 0.0.4'
  require 'scriptingutils'
  quit('Hello World!',0)

In the .gemspec file I have:

  spec.add_dependency('scriptingutils',[">= 0.0.4"])

and in the top directory, where the Rakefile is, I have a file Gemfile,
containing:

  source "http://wybo.xs4all.nl/wdgems"
  gem "scriptingutils", ">= 0.0.4"

Still, when I try to install, I get the message:
  ERROR: While executing gem ... (Gem::DependencyError)
      Unable to resolve dependencies: hello requires scriptingutils
  (>= 0.0.4)

It helps when I first run:
  gem sources --add http://wybo.xs4all.nl/wdgems/

But that information is already in the Gemfile, and I don't want users
of the gem to add that source explicitly, of course. How can I make gem
to read the Gemfile?

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Wybo