On Stock Kali 2.0 (after apt-get upgrade), the following command errors ./egghunter.rb --list-formats. Adding the require 'msfenv' to the file alleviates the issue.
root@kali:/usr/share/metasploit-framework/tools/exploit# ./egghunter.rb --list-formats
/usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- rkelly (LoadError)
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/metasploit-framework/lib/rex/proto/http/response.rb:5:in `<top (required)>'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/metasploit-framework/lib/rex/proto/http.rb:4:in `<top (required)>'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/metasploit-framework/lib/rex/proto.rb:2:in `<top (required)>'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/metasploit-framework/lib/rex.rb:79:in `<top (required)>'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/metasploit-framework/lib/msf/core.rb:17:in `<top (required)>'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/share/metasploit-framework/lib/msf/base.rb:17:in `<top (required)>'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from ./egghunter.rb:9:in `<main>'
not strictly required, these conversions keep us
up to date with latest rspec conventions and best practices
which will prevent use from having to convert them when they become
deprecated later