Make Atom smarter about guessing if a file uses soft or hard tabs

Previously, block commits would screw up tab prediction. For example:

```
/**ruby
  * I'm a docblock directly at the start of a file with a space to line up the docblock
  */
```

Atom would previously assume this file uses softTabs because of the block comment using leading spaces. Now Atom will ignore comments when figuring out if a file uses soft or hard tabs.