added small tweak to catch the {} returned by calling ckit, which was gi...

...ving an hash to integer conversion error

Was getting this stack trace:

```
/Users/jfox/.rvm/gems/ruby-1.9.3-p429@Animoto/gems/chemistrykit-1.2.0/bin/ckit:13:in `exit': can't convert Hash into Integer (TypeError)
from /Users/jfox/.rvm/gems/ruby-1.9.3-p429@Animoto/gems/chemistrykit-1.2.0/bin/ckit:13:in `<top (required)>'
from /Users/jfox/.rvm/gems/ruby-1.9.3-p429@Animoto/bin/ckit:19:in `load'
from /Users/jfox/.rvm/gems/ruby-1.9.3-p429@Animoto/bin/ckit:19:in `<main>'
from /Users/jfox/.rvm/gems/ruby-1.9.3-p429@Animoto/bin/ruby_noexec_wrapper:14:in `eval'
from /Users/jfox/.rvm/gems/ruby-1.9.3-p429@Animoto/bin/ruby_noexec_wrapper:14:in `<main>'
```

running `ckit` seemed to return an empty hash, so just added a catch for that, not sure why the tests were not picking it up, perhaps we never just ran that.