Switch to minitest for consistent output between Ruby versions

In Ruby 2.0, `test/unit` activates a fancy output style for terminals
that doesn't look well in Travis logs. I could disable it with the
`--jobs-status=normal` test optiont, but that option isn't supported in
Ruby 1.8.7.

Instead of dealing with inconsistencies between test support in
different Ruby versions, I'm simply switching to a fixed version of
Minitest.

Gemfile

@@ -1,5 +1,6 @@
 source 'https://rubygems.org'
 
+gem 'minitest'
 gem 'ronn', :platform => :mri
 gem 'aruba', '~> 0.5.3'
 gem 'cucumber', '~> 1.2.1'

Gemfile.lock

@@ -33,6 +33,7 @@ GEM
       bouncy-castle-java (>= 1.5.0146.1)
     json (1.8.0)
     json (1.8.0-java)
+    minitest (5.0.5)
     multi_json (1.7.7)
     mustache (0.99.4)
     rack (1.4.1)
@@ -65,6 +66,7 @@ DEPENDENCIES
   hub!
   jruby-openssl
   json
+  minitest
   rake
   ronn
   sinatra

Rakefile

@@ -31,9 +31,7 @@ task :default => [:test, :features]
 
 Rake::TestTask.new do |t|
   t.libs << 'test'
-  t.ruby_opts << '-rubygems'
   t.pattern = 'test/**/*_test.rb'
-  t.verbose = false
 end
 
 task :features do

test/context_test.rb

@@ -1,6 +1,6 @@
 require 'helper'
 
-class ContextTest < Test::Unit::TestCase
+class ContextTest < Minitest::Test
   class Context
     include Hub::Context
 

test/helper.rb

@@ -1,4 +1,4 @@
-require 'test/unit'
+require 'minitest/autorun'
 require 'hub'
 
 # We're checking for `open` in our tests
@@ -28,7 +28,7 @@ Hub::Commands.extend Module.new {
   end
 }
 
-class Test::Unit::TestCase
+class Minitest::Test
   # Shortcut for creating a `Hub` instance. Pass it what you would
   # normally pass `hub` on the command line, e.g.
   #

test/hub_test.rb

@@ -1,5 +1,5 @@
 require 'helper'
-require 'webmock/test_unit'
+require 'webmock/minitest'
 require 'rbconfig'
 require 'yaml'
 require 'forwardable'
@@ -19,7 +19,7 @@ WebMock::BodyPattern.class_eval do
   end
 end
 
-class HubTest < Test::Unit::TestCase
+class HubTest < Minitest::Test
   extend Forwardable
 
   if defined? WebMock::API

test/standalone_test.rb

@@ -3,7 +3,7 @@ require 'hub/standalone'
 require 'fileutils'
 require 'stringio'
 
-class StandaloneTest < Test::Unit::TestCase
+class StandaloneTest < Minitest::Test
   include FileUtils
 
   def setup