Move spoon dep to Gemfile

By moving it to the Gemfile & using platform we're able avoid installing
spoon for other Ruby implementations.

Gemfile

@@ -2,6 +2,10 @@ source "http://rubygems.org"
 
 gemspec
 
+platform :jruby do
+  gem 'spoon', '~> 0.0.1'
+end
+
 group :development do
   gem 'parka'
   gem 'rake'

Gemfile.lock

@@ -2,7 +2,6 @@ PATH
   remote: .
   specs:
     foreman (0.36.1)
-      spoon (~> 0.0.1)
       term-ansicolor (~> 1.0.7)
       thor (>= 0.13.6)
 
@@ -65,3 +64,4 @@ DEPENDENCIES
   rr (~> 1.0.2)
   rspec (~> 2.0)
   rubyzip
+  spoon (~> 0.0.1)

foreman.gemspec

@@ -18,5 +18,4 @@ Gem::Specification.new do |gem|
 
   gem.add_dependency 'term-ansicolor', '~> 1.0.7'
   gem.add_dependency 'thor',           '>= 0.13.6'
-  gem.add_dependency 'spoon',          '~> 0.0.1'
 end