Fix render text deprecation warning

`render text:` is no longer a valid way to render just text content. The
correct way is to use `render plain:`. `render text:` is deprecated.

Author: eileencodes

lib/action_controller/caching/actions.rb

@@ -173,7 +173,7 @@ def around(controller)
             body = controller._save_fragment(cache_path.path, @store_options)
           end
 
-          body = controller.render_to_string(text: body, layout: true) unless cache_layout
+          body = controller.render_to_string(plain: body, layout: true) unless cache_layout
 
           controller.response_body = body
           controller.content_type = Mime[cache_path.extension || :html]

test/caching_test.rb

@@ -50,27 +50,27 @@ class ActionCachingTestController < CachingController
 
   def index
     @cache_this = MockTime.now.to_f.to_s
-    render text: @cache_this
+    render plain: @cache_this
   end
 
   def redirected
     redirect_to action: 'index'
   end
 
   def forbidden
-    render text: 'Forbidden'
+    render plain: 'Forbidden'
     response.status = '403 Forbidden'
   end
 
   def with_layout
     @cache_this = MockTime.now.to_f.to_s
     @title = nil
-    render text: @cache_this, layout: true
+    render plain: @cache_this, layout: true
   end
 
   def with_format_and_http_param
     @cache_this = MockTime.now.to_f.to_s
-    render text: @cache_this
+    render plain: @cache_this
   end
 
   def with_symbol_format
@@ -87,7 +87,7 @@ def record_not_found
   end
 
   def four_oh_four
-    render text: "404'd!", status: 404
+    render plain: "404'd!", status: 404
   end
 
   def simple_runtime_error
@@ -118,7 +118,7 @@ def expire_with_url_string
   end
 
   def streaming
-    render text: 'streaming', stream: true
+    render plain: 'streaming', stream: true
   end
 
   def invalid