ruby isn't streaming instruments output

Rakefile

task :test => :coffeescript do
  template = '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/Library/Instruments/PlugIns/AutomationInstrument.bundle/Contents/Resources/Automation.tracetemplate'
  app = '~/dev/ios/TravisCI/build/TravisCI.app'
  variables = {
    'UIASCRIPT' => '~/dev/ios/TravisCI/automation/uiautomation.js',
    'UIARESULTSPATH' => '~/dev/ios/TravisCI/automation/results'
  }.map{|key,val| "-e #{key} #{val}"}.join(' ')

  STDOUT.sync = true
  Open3.popen2e("instruments -t #{template} #{app} #{variables}") do |stdin, stdout, wait_thr|
    stdout.each_line do |line|
      puts line
    end
    puts "status: #{wait_thr.value}"
  end
end