Wrong indentation of case do clause with pipeline

Hi everyone,

This issue happens with the `case do`. Elixir indentation should be this one:
```
variable
|> case do
  nil ->
    :noop
  _ ->
    :ok
end
```

But the elixir-mode does this, it places four spaces:
```
variable
|> case do
    nil ->
      :noop
    _ ->
      :ok
end
```
