Use Elixir v1.5's streamlined child specs in docs (#3233)

* Use Elixir v1.5's streamlined child specs in Endpoint docs

* Use Elixir v1.5's streamlined child specs in mix ecto.gen.repo docs

guides/endpoint.md

@@ -10,7 +10,7 @@ defmodule Hello.Application do
     #...
 
     children = [
-      supervisor(HelloWeb.Endpoint, []),
+      HelloWeb.Endpoint
     ]
 
     opts = [strategy: :one_for_one, name: Hello.Supervisor]

guides/phoenix_mix_tasks.md

@@ -713,13 +713,14 @@ We certainly should follow the instructions and add our new repo to our supervis
 ```elixir
 . . .
 children = [
-  # Start the endpoint when the application starts
-  supervisor(HelloWeb.Endpoint, []),
   # Start the Ecto repository
-  worker(Hello.Repo, []),
+  Hello.Repo,
+  # Start the endpoint when the application starts
+  HelloWeb.Endpoint,
+  # Starts a worker by calling: Hello.Worker.start_link(arg)
+  # {Hello.Worker, arg},
   # Here you could define other workers and supervisors as children
-  # worker(Hello.Worker, [arg1, arg2, arg3]),
-  worker(OurCustom.Repo, []),
+  OurCustom.Repo
 ]
 . . .
 ```

lib/phoenix/endpoint.ex

@@ -38,7 +38,9 @@ defmodule Phoenix.Endpoint do
   to the supervision tree in generated applications. Endpoints can be
   added to the supervision tree as follows:
 
-      supervisor(YourApp.Endpoint, [])
+      children = [
+        YourApp.Endpoint
+      ]
 
   ### Endpoint configuration