Move dev dependencies from Gemfile to the gemspec: rake, puma, mocha

Gemfile

@@ -1,9 +1,2 @@
-source 'http://rubygems.org'
+source 'https://rubygems.org'
 gemspec
-
-group :test do
-  gem 'rake'
-  gem 'puma'
-  gem 'mocha'
-end
-

Gemfile.lock

@@ -11,7 +11,7 @@ PATH
       websocket-driver (= 0.5.4)
 
 GEM
-  remote: http://rubygems.org/
+  remote: https://rubygems.org/
   specs:
     actionpack (4.2.3)
       actionview (= 4.2.3)

actioncable.gemspec

@@ -19,6 +19,10 @@ Gem::Specification.new do |s|
   s.add_dependency 'em-hiredis',       '~> 0.3.0'
   s.add_dependency 'redis',            '~> 3.0'
 
+  s.add_development_dependency 'rake'
+  s.add_development_dependency 'puma'
+  s.add_development_dependency 'mocha'
+
   s.files = Dir['README', 'lib/**/*']
   s.has_rdoc = false