Gemfile: remove groups

We plan to use SimpleCov and Bundler.require gets in the way. Without it Gemfile
groups are useless, so I am removing them.

I am also removing the silly `Bundler/OrderedGems` cop, one of the most useless
cops you can add.

.rubocop.yml

@@ -52,3 +52,6 @@ Style/SymbolArray:
 
 Metrics/LineLength:
   Max: 90
+
+Bundler/OrderedGems:
+  Enabled: false

Gemfile

@@ -1,21 +1,12 @@
 source 'https://rubygems.org'
 gemspec
+
 gem 'rake', '~> 10.0'
+gem 'gist'
+gem 'yard'
+gem 'rspec', '~> 3.8.0'
 
-group :development do
-  gem 'gist'
-  gem 'yard'
-
-  # Rubocop supports only >=2.2.0
-  if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.2.0')
-    gem 'rubocop', '= 0.65.0', require: false
-  end
-end
-
-group :test do
-  gem 'rspec', '~> 3.8.0'
-end
-
-group :development, :test do
-  gem 'simplecov', '~> 0.8.0'
+# Rubocop supports only >=2.2.0
+if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.2.0')
+  gem 'rubocop', '= 0.65.0', require: false
 end