Pre-load the gem resource to override the global gem method.

This seems problematic to me in general. We should probably not
override global methods. Renaming this to rubygem and providing a
deprecated alias seems like the right thing to do.

Signed-off-by: Ryan Davis <zenspider@chef.io>

lib/inspec/resource.rb

@@ -110,3 +110,5 @@ end
 
 # Many resources use FilterTable.
 require "inspec/utils/filter"
+# conflicts with global `gem` method so we need to pre-load this.
+require "inspec/resources/gem"

lib/inspec/resources/gem.rb

@@ -2,7 +2,7 @@ require "inspec/resources/command"
 
 module Inspec::Resources
   class GemPackage < Inspec.resource(1)
-    name "gem"
+    name "gem" # TODO: rename to "rubygem" and provide alias
     supports platform: "unix"
     supports platform: "windows"
     desc "Use the gem InSpec audit resource to test if a global gem package is installed."