stop using removed `render :text`

Follow up to 79a5ea9ead

actionpack/test/dispatch/routing/ipv6_redirect_test.rb

@@ -7,7 +7,7 @@ class IPv6IntegrationTest < ActionDispatch::IntegrationTest
   class ::BadRouteRequestController < ActionController::Base
     include Routes.url_helpers
     def index
-      render text: foo_path
+      render plain: foo_path
     end
 
     def foo

actionview/test/ujs/server.rb

@@ -96,7 +96,7 @@ class TestsController < ActionController::Base
 
       render html: html.html_safe
     else
-      render text: "ERROR: #{request.path} requested without ajax", status: 404
+      render plain: "ERROR: #{request.path} requested without ajax", status: 404
     end
   end
 end

activesupport/lib/active_support/notifications.rb

@@ -13,7 +13,7 @@ module ActiveSupport
   # To instrument an event you just need to do:
   #
   #   ActiveSupport::Notifications.instrument('render', extra: :information) do
-  #     render text: 'Foo'
+  #     render plain: 'Foo'
   #   end
   #
   # That first executes the block and then notifies all subscribers once done.
@@ -48,7 +48,7 @@ module ActiveSupport
   # The block is saved and will be called whenever someone instruments "render":
   #
   #   ActiveSupport::Notifications.instrument('render', extra: :information) do
-  #     render text: 'Foo'
+  #     render plain: 'Foo'
   #   end
   #
   #   event = events.first

guides/source/action_mailer_basics.md

@@ -400,7 +400,7 @@ class UserMailer < ApplicationMailer
     mail(to: @user.email,
          subject: 'Welcome to My Awesome Site') do |format|
       format.html { render 'another_template' }
-      format.text { render text: 'Render text' }
+      format.text { render plain: 'Render text' }
     end
   end
 end