Indent to opposite direction on right-to-left line

[benbro]

[Describe the issue]
On lines with direction:rtl the indent left button actually indent right.
This is noticeable when using multilevel lists and trying to indent to create a new level.

Steps for Reproduction

1. Visit http://quilljs.com/docs/formats/
2. Type 'abc'
3. Click on the direction button to set the line direction to right-to-left
4. Click on the indent left (-1) button

Expected behavior: [expected]
The text should indent left

Actual behavior: [actual]
Nothing happened.
Clicking on the indent right button indents left but that's counter intuitive.

Platforms:
Chrome 52 on Windows 7

Version: [version]
1.0.0-rc0