Fix some new RuboCop warnings

Author: lcreid

demo/config/environments/development.rb

@@ -16,7 +16,7 @@
 
   # Enable/disable caching. By default caching is disabled.
   # Run rails dev:cache to toggle caching.
-  if Rails.root.join("tmp/caching-dev.txt").exist?
+  if Rails.root.join("tmp", "caching-dev.txt").exist?
     config.action_controller.perform_caching = true
 
     config.cache_store = :memory_store

test/bootstrap_form_test.rb

@@ -352,7 +352,7 @@ class BootstrapFormTest < ActionView::TestCase
   end
 
   test "allows to set custom default form attributes via configuration" do
-    BootstrapForm.config.stubs(:default_form_attributes).returns({ foo: "bar" })
+    BootstrapForm.config.stubs(:default_form_attributes).returns(foo: "bar")
     expected = <<-HTML.strip_heredoc
       <form accept-charset="UTF-8" action="/users" class="new_user" foo="bar" id="new_user" method="post">
         #{'<input name="utf8" type="hidden" value="&#x2713;"/>' unless ::Rails::VERSION::STRING >= '6'}