guard file update for 4.0

Guardfile

@@ -8,7 +8,7 @@ guard 'rails' do
 end
 
 
-guard :rspec do
+guard :rspec, cmd: "bundle exec rspec" do
   watch(%r{^spec/.+_spec\.rb$})
   watch(%r{^lib/(.+)\.rb$})     { |m| "spec/lib/#{m[1]}_spec.rb" }
   watch('spec/spec_helper.rb')  { "spec" }