Update cucumber dependency

In the process, we remove our cucumber docstrings monkey patch. It
does not work anymore and it was not a so good idea.

features/cli/usage.feature

@@ -13,4 +13,5 @@ Feature: CLI usage
           -d, --debug                      enable debug mode
           -n, --dry-run                    enable dry run mode
           -t, --target HOST                target host
+
       """

features/support/env_cucumber_doc_string.rb

@@ -1,23 +0,0 @@
-require 'cucumber/formatter/pretty'
-
-module Cucumber
-  module Ast
-    class DocString
-      alias :old_initialize :initialize
-
-      def initialize(string, content_type)
-        old_initialize(string + "\n", content_type)
-      end
-    end
-  end
-
-  module Formatter
-    class Pretty
-      alias :old_doc_string :doc_string
-
-      def doc_string(string)
-        old_doc_string(string.chomp)
-      end
-    end
-  end
-end

producer-core.gemspec

@@ -21,7 +21,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'net-sftp',  '~> 2.1'
 
   s.add_development_dependency 'rspec',         '~> 3.1'
-  s.add_development_dependency 'cucumber',      '~> 1.3'
+  s.add_development_dependency 'cucumber',      '~> 2.0'
   s.add_development_dependency 'aruba',         '~> 0.5'
   s.add_development_dependency 'cucumber-sshd', '~> 0.1'
   s.add_development_dependency 'rake',          '~> 10.1'