Add correct paths to $LOAD_PATH (#1169)

The `bin/setup` script was failing due to being unable to find the
required files in `demo/config/application.rb`. It looks like the
file references we're nested one level to deep.

demo/config/boot.rb

@@ -1,5 +1,5 @@
 # Set up gems listed in the Gemfile.
-ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../../Gemfile', __dir__)
+ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __dir__)
 
 require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])
-$LOAD_PATH.unshift File.expand_path('../../../lib', __dir__)
+$LOAD_PATH.unshift File.expand_path('../../lib', __dir__)