Fix alias ordering error

[rattrayalex]

I encountered an error because a yaml anchor was not detected before its reference in YAML's document.toString(). This wasn't because of an error in the yaml document at hand, but just because of the representation passed to the YAML library (which only gets one part at a time) so this verification should not take place by default.

Note this would conflict with https://github.com/grantila/yaml-diff-patch/pull/5; if you choose to merge that PR, this should have the options merged in.