Incorrect indentation when there's a comma and a newline

Originally reported here: https://github.com/atom/language-ruby/issues/7

Example:

``` ruby
class Example
  def test
    ["a",
     "b"]
  end
end
```

After running `Indent Selection`:

``` ruby
class Example
  def test
    ["a",
       "b"]
    end
  end
```
