$./rails/railties/exe/rails -v
/usr/local/var/rbenv/versions/2.2.2/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- concurrent/map (LoadError)
from /usr/local/var/rbenv/versions/2.2.2/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/moonstruckdrops/rails/activesupport/lib/active_support/inflector/inflections.rb:1:in `<top (required)>'
from /usr/local/var/rbenv/versions/2.2.2/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /usr/local/var/rbenv/versions/2.2.2/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/moonstruckdrops/rails/activesupport/lib/active_support/inflections.rb:1:in `<top (required)>'
(省略)
$cd my_app
$bin/rails s
=> Booting WEBrick
=> Rails 5.0.0.alpha application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
[2015-11-06 00:00:05] INFO WEBrick 1.3.1
[2015-11-06 00:00:05] INFO ruby 2.2.2 (2015-04-13) [x86_64-darwin14]
[2015-11-06 00:00:05] INFO WEBrick::HTTPServer#start: pid=14583 port=3000