Upgrade various Rails 5.0 references to 5.1

RC1 is out, `5-1-stable` has been created, figured it was time to start
updating this stuff :)

[ci skip]

guides/source/_welcome.html.erb

@@ -10,12 +10,13 @@
 </p>
 <% else %>
 <p>
-  These are the new guides for Rails 5.0 based on <a href="https://github.com/rails/rails/tree/<%= @version %>"><%= @version %></a>.
+  These are the new guides for Rails 5.1 based on <a href="https://github.com/rails/rails/tree/<%= @version %>"><%= @version %></a>.
   These guides are designed to make you immediately productive with Rails, and to help you understand how all of the pieces fit together.
 </p>
 <% end %>
 <p>
 The guides for earlier releases:
+<a href="http://guides.rubyonrails.org/v5.0/">Rails 5.0</a>,
 <a href="http://guides.rubyonrails.org/v4.2/">Rails 4.2</a>,
 <a href="http://guides.rubyonrails.org/v4.1/">Rails 4.1</a>,
 <a href="http://guides.rubyonrails.org/v4.0/">Rails 4.0</a>,

guides/source/command_line.md

@@ -63,7 +63,7 @@ With no further work, `rails server` will run our new shiny Rails app:
 $ cd commandsapp
 $ bin/rails server
 => Booting Puma
-=> Rails 5.0.0 application starting in development on http://0.0.0.0:3000
+=> Rails 5.1.0 application starting in development on http://0.0.0.0:3000
 => Run `rails server -h` for more startup options
 Puma starting in single mode...
 * Version 3.0.2 (ruby 2.3.0-p0), codename: Plethora of Penguin Pinatas
@@ -294,7 +294,7 @@ If you wish to test out some code without changing any data, you can do that by
 
 ```bash
 $ bin/rails console --sandbox
-Loading development environment in sandbox (Rails 5.0.0)
+Loading development environment in sandbox (Rails 5.1.0)
 Any modifications you make will be rolled back on exit
 irb(main):001:0>
 ```
@@ -428,10 +428,10 @@ INFO: You can also use `bin/rails -T`  to get the list of tasks.
 ```bash
 $ bin/rails about
 About your application's environment
-Rails version             5.0.0
+Rails version             5.1.0
 Ruby version              2.2.2 (x86_64-linux)
 RubyGems version          2.4.6
-Rack version              1.6
+Rack version              2.0.1
 JavaScript Runtime        Node.js (V8)
 Middleware                Rack::Sendfile, ActionDispatch::Static, ActionDispatch::Executor, #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x007ffd131a7c88>, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::RemoteIp, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, Rack::Head, Rack::ConditionalGet, Rack::ETag
 Application root          /home/foobar/commandsapp

guides/source/debugging_rails_applications.md

@@ -313,7 +313,7 @@ For example:
 
 ```bash
 => Booting Puma
-=> Rails 5.0.0 application starting in development on http://0.0.0.0:3000
+=> Rails 5.1.0 application starting in development on http://0.0.0.0:3000
 => Run `rails server -h` for more startup options
 Puma starting in single mode...
 * Version 3.4.0 (ruby 2.3.1-p112), codename: Owl Bowl Brawl
@@ -445,11 +445,11 @@ then `backtrace` will supply the answer.
 --> #0  ArticlesController.index
       at /PathToProject/app/controllers/articles_controller.rb:8
     #1  ActionController::BasicImplicitRender.send_action(method#String, *args#Array)
-      at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/basic_implicit_render.rb:4
+      at /PathToGems/actionpack-5.1.0/lib/action_controller/metal/basic_implicit_render.rb:4
     #2  AbstractController::Base.process_action(action#NilClass, *args#Array)
-      at /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb:181
+      at /PathToGems/actionpack-5.1.0/lib/abstract_controller/base.rb:181
     #3  ActionController::Rendering.process_action(action, *args)
-      at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/rendering.rb:30
+      at /PathToGems/actionpack-5.1.0/lib/action_controller/metal/rendering.rb:30
 ...
 ```
 
@@ -461,7 +461,7 @@ context.
 ```
 (byebug) frame 2
 
-[176, 185] in /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb
+[176, 185] in /PathToGems/actionpack-5.1.0/lib/abstract_controller/base.rb
    176:       # is the intended way to override action dispatching.
    177:       #
    178:       # Notice that the first argument is the method to be dispatched
@@ -676,7 +676,7 @@ Ruby instruction to be executed -- in this case, Active Support's `week` method.
 ```
 (byebug) step
 
-[49, 58] in /PathToGems/activesupport-5.0.0/lib/active_support/core_ext/numeric/time.rb
+[49, 58] in /PathToGems/activesupport-5.1.0/lib/active_support/core_ext/numeric/time.rb
    49:
    50:   # Returns a Duration instance matching the number of weeks provided.
    51:   #

guides/source/getting_started.md

@@ -127,7 +127,7 @@ run the following:
 $ rails --version
 ```
 
-If it says something like "Rails 5.0.0", you are ready to continue.
+If it says something like "Rails 5.1.0", you are ready to continue.
 
 ### Creating the Blog Application