Add `silence_stream` method removed in Rails 5

Ref: https://github.com/rails/rails/commit/481e49c64f790e46f4aff3ed539ed227d2eb46cb

`silence_stream` was deprecated in Rails 4.2 and removed in Rails 5
because it was not thread safe. Paperclip is not running the tests in
threaded mode, it's safe to add the method back in a test support
module.

spec/spec_helper.rb

@@ -36,6 +36,7 @@ RSpec.configure do |config|
   config.include Assertions
   config.include ModelReconstruction
   config.include TestData
+  config.include Reporting
   config.extend VersionHelper
   config.mock_framework = :mocha
   config.before(:all) do

spec/support/reporting.rb

+module Reporting
+  def silence_stream(stream)
+    old_stream = stream.dup
+    stream.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
+    stream.sync = true
+    yield
+  ensure
+    stream.reopen(old_stream)
+    old_stream.close
+  end
+end