Trying to avoid the RAISED \xFF from ASCII-8BIT to UTF-8 issue

I'm getting `RAISED "\xFF" from ASCII-8BIT to UTF-8` from this line in my project.

```
INFO    Compiled my_app/templates/profile_information/account_information/identity/edit.js  (117ms)  (pid 37296)
INFO    Compiled my_app/templates/profile_information/account_information/identity/show.js  (110ms)  (pid 37296)
DEBUG   Compiling help.jpg to /Users/mario/Projects/my_app/spec/tmp/assets/help.jpg
ERROR   ERROR: compiling /Users/mario/Projects/my_app/app/assets/javascripts/my_app/templates/profile_information/payment_methods/_form.jst.eco.haml RAISED "\xFF" from ASCII-8BIT to UTF-8
ERROR   Backtrace: /Users/mario/.rbenv/versions/1.9.3-p194/lib/ruby/gems/1.9.1/gems/jasmine-rails-0.4.5/lib/jasmine_rails/offline_asset_paths.rb:28:in `write'
```

It's get fix by opening the file in binary mode ('wb' instead of 'w').