Lines -> Auto Indent (editor:auto-indent) misinterprets case branches

atom: ver `1.6.0-beta6-8bd4c99`
language-elixir: ver `0.11.1`

It seems auto-indent does not properly unindent branches of `case`.

Instead of

``` elixir
defmodule Demo do
def demo(value) do
case value do
:one ->
do_one
:two ->
do_two
:three ->
do_three
end
end
end
```

you get

``` elixir
defmodule Demo do
def demo(value) do
case value do
:one ->
do_one
:two ->
do_two
:three ->
do_three
end
end
end
```