Remove duplicate rake dependency in gemspec

omnibus.gemspec

@@ -24,7 +24,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency 'mixlib-shellout', '~> 1.3'
   gem.add_dependency 'mixlib-config',   '~> 2.1'
   gem.add_dependency 'ohai',            '~> 6.12'
-  gem.add_dependency 'rake',            '>= 0.9'
+  gem.add_dependency 'rake'
   gem.add_dependency 'fpm',             '~> 1.0.0'
   gem.add_dependency 'uber-s3'
   gem.add_dependency 'thor',            '>= 0.16.0'
@@ -33,5 +33,4 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency 'rubocop', '~> 0.18'
   gem.add_development_dependency 'bundler'
-  gem.add_development_dependency 'rake'
 end