Fix osx `launch.browsers` if mdfind returns multiples results

If (like me) you have more than just one app foreach browsers (like you have 2 Firefox.app in different places), this package just throw an error because it try to use a multiple line result returned by mdfind as path for the app.

Example:

```
❯ mdfind "kMDItemCFBundleIdentifier=="com.apple.Safari""
/Applications/Safari.app
/Volumes/Backup/Applications/Safari.app
```

Here you can see I've 2 lines & it's completely making this awesome package broken.
**So using `head -1` help to be sure that you just get the first result.**