Setting approprite file mode to avoid ascii_to_utf8 issue

I've encountered an issue while running heaven + capistrano on my end. 

The worker crashed with this [stacktrace](https://gist.github.com/balbeko/b78bdd1dd5e7d74e1cf9) while running capistrano+grunt task. 

According to `"\xE2" from ASCII-8BIT to UTF-8` issue, I suggest that `npm` or `grunt` had sent me out some odd output with Unicode chars.

So i feel that patching this in upstream might be useful for any further integrations of `heaven` with any kind of tools.

Thanks, 
Serhii