Added multiline ruby syntax highlighting when lines end with comma.

As described in the documentation, we don't need backslash for these lines.
http://rdoc.info/gems/slim/file/README.md#Control_code_-

Example
```
= link_to "Long link text here.............",
     long_controller_and_action_names_path

/ Instead of

= link_to "Long link text here.............", \
     long_controller_and_action_names_path

```