commands/plugin: list plugins uses Bundler

plugins/commands/plugin/action/list_plugins.rb

@@ -1,4 +1,3 @@
-require "rubygems"
 require "set"
 
 module VagrantPlugins
@@ -23,8 +22,7 @@ module VagrantPlugins
           # Go through the plugins installed in this environment and
           # get the latest version of each.
           installed_map = {}
-          env[:gem_helper].with_environment do
-            Gem::Specification.find_all.each do |spec|
+          Bundler.load.specs.each do |spec|
             # Ignore specs that aren't in our installed list
             next if !installed.include?(spec.name)
 
@@ -35,7 +33,6 @@ module VagrantPlugins
 
             installed_map[spec.name] = spec
           end
-          end
 
           # Output!
           if installed_map.empty?