Remove ContentLength middleware from the defaults.

ContentLength is not part of the rack SPEC since rack/rack@86ddc7a6ec
If you want it, just add it as a middleware in your config.

railties/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Remove ContentLength middleware from the defaults.  If you want it, just
+    add it as a middleware in your config.
+
+    *Egg McMuffin*
+
 *   Make it possible to customize the executable inside rerun snippets.
 
     *Yves Senn*

railties/lib/rails/commands/server.rb

@@ -78,7 +78,6 @@ def start
 
     def middleware
       middlewares = []
-      middlewares << [::Rack::ContentLength]
 
       # FIXME: add Rack::Lock in the case people are using webrick.
       # This is to remain backwards compatible for those who are