added spec to prove cannot() record deletion bug
reverted to previous query negation implementation
raise exception when unable to invert cannot query + spec
removed copypasta in spec
made negative queries work with plucky queries as parameter
Merge pull request #1 from codegourmet/bogn/topic/negative_queries

mm adapter: fixed bug where data loss would occur with cannot() rules. See the comments on this [commit](https://github.com/juggler/cancan/commit/0a2556bf557334a8b2e002ad573692d47dc9d54a#commitcomment-4112111) that was also merged into this repo for reference.