Add gem dependencies from our previous bundler setup

I haven't recently thought about the rationale for any of these
dependencies. I'm just copying our previous setup in an attempt to get a
working gem.

api-spec.gemspec

@@ -8,4 +8,11 @@ Gem::Specification.new do |s|
   s.files       = [ 'lib/api-spec.rb' ]
   s.homepage    = 'https://github.com/nutshellcrm/api-spec'
   s.license       = 'MIT'
+
+  s.add_runtime_dependency 'cucumber', '~> 1.3.2'
+  s.add_runtime_dependency 'rspec', '~> 2.13.0'
+  s.add_runtime_dependency 'faraday', '~> 0.8.7'
+
+  s.add_runtime_dependency 'json_spec', '~> 1.1.1'
+  s.add_runtime_dependency 'json', '~> 1.8.0'
 end