Require forwardable explicitly

[kamil89]

Version 0.5.0 has introduced a bug which prevents soapforce to be loaded properly in some cases by using Forwardable module without requiring it explicitly.

Irb output:

soapforce|master ⇒ irb
irb(main):001:0> require "soapforce"
NameError: uninitialized constant Soapforce::Result::Forwardable
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/soapforce-0.5.0/lib/soapforce/result.rb:3:in `<class:Result>'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/soapforce-0.5.0/lib/soapforce/result.rb:2:in `<module:Soapforce>'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/soapforce-0.5.0/lib/soapforce/result.rb:1:in `<top (required)>'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/soapforce-0.5.0/lib/soapforce.rb:7:in `<top (required)>'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:127:in `require'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:127:in `rescue in require'
  from /Users/kamil/.rbenv/versions/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:40:in `require'
  from (irb):1
  from /Users/kamil/.rbenv/versions/2.3.0/bin/irb:11:in `<main>'
irb(main):002:0> require "forwardable"
=> true
irb(main):003:0> require "soapforce"
=> true

Adding simple require "forwardable" fixes the bug. Similar issue in monetize https://github.com/RubyMoney/monetize/issues/44

[jheth]

@kamil89 Thanks!