[bundler/bundler] Removed the environmental variables that are BUNDLE_USER_*.

It's affect with rspec examples and broke them.

https://github.com/bundler/bundler/commit/355a922073

spec/bundler/spec_helper.rb

@@ -101,6 +101,7 @@ RSpec.configure do |config|
     Spec::Rubygems.setup
     ENV["RUBYOPT"] = "#{ENV["RUBYOPT"]} -r#{Spec::Path.spec_dir}/support/hax.rb"
     ENV["BUNDLE_SPEC_RUN"] = "true"
+    ENV["BUNDLE_USER_CONFIG"] = ENV["BUNDLE_USER_CACHE"] = ENV["BUNDLE_USER_PLUGIN"] = nil
 
     # Don't wrap output in tests
     ENV["THOR_COLUMNS"] = "10000"