chore: cleanup gemspec/Gemfile deps

Gemfile

@@ -1,23 +1,19 @@
 source 'https://rubygems.org'
 
-gem 'jruby-openssl', '~> 0.10.5', platforms: :jruby
-gem 'rake', '>= 12.0'
-gem 'yard', '>= 0.9.11'
-
 group :development do
-  gem 'benchmark-ips'
-  gem 'kramdown'
-  gem 'memory_profiler'
-  gem 'pry'
+  gem 'benchmark-ips', require: false
+  gem 'memory_profiler', require: false
+  gem 'rubocop', '>= 0.58.2', '< 0.69.0', require: false
+  gem 'pry', require: false
+  gem 'yard', '>= 0.9.11', require: false
 end
 
 group :test do
   gem 'coveralls_reborn', '~> 0.19.0', require: false
-  gem 'rack-test'
-  gem 'rspec', '~> 3.5'
-  gem 'rack-freeze'
-  gem 'rubocop', '>= 0.58.2', '< 0.69.0', platforms: %i[ruby_22 ruby_23 ruby_24]
-  gem 'simplecov-lcov'
+  gem 'rack-test', require: false
+  gem 'rspec', '~> 3.5', require: false
+  gem 'rack-freeze', require: false
+  gem 'simplecov-lcov', require: false
 end
 
 gemspec

omniauth.gemspec

@@ -7,9 +7,10 @@ require 'omniauth/version'
 Gem::Specification.new do |spec|
   spec.add_dependency 'hashie', ['>= 3.4.6']
   spec.add_dependency 'rack', '>= 2.2.3'
-  spec.add_development_dependency 'bundler', '~> 2.0'
   spec.add_dependency 'rack-protection'
-  spec.add_development_dependency 'rake', '~> 12.0'
+  spec.add_dependency 'jruby-openssl', '~> 0.10.5' if $platform.to_s == 'java'
+  spec.add_development_dependency 'bundler', '~> 2.0'
+  spec.add_development_dependency 'rake', '~> 13.0'
   spec.authors       = ['Michael Bleigh', 'Erik Michaels-Ober', 'Tom Milewski']
   spec.description   = 'A generalized Rack framework for multiple-provider authentication.'
   spec.email         = ['michael@intridea.com', 'sferik@gmail.com', 'tmilewski@gmail.com']