<img width="1608" alt="SCR-20230806-cyrg"
src="https://github.com/zed-industries/zed/assets/19867440/2491c4bc-5797-4417-9633-08c136b4e8fe">

I noticed we weren't highlghting bash files if the shebang line didn't
exist. After checking, it looks like the `.` were accidentally added to
the `path_suffixes` list. This PR fixes that and adds in support for
`cmd-/` to trigger line comments.

<img width="1608" alt="SCR-20230806-czxh"
src="https://github.com/zed-industries/zed/assets/19867440/37dd0c8e-c4e7-49e2-9997-9dd8145f460e">


Release Notes:

- Fixed a bug where shell files weren't syntax highlighted if a shebang
didn't exist.
- Added support for `cmd-/` to add line comments to shell files.