Check against Map.IMap not `Map` and friends

Somewhere on the path to 3.2 using `Std.id( obj, AbstractType )` has become disallowed, and I gather it never worked anyway - hence testing every type manually before.  

Checking against the `Map.IMap` interface does work.  (Though it is moving to `haxe.Constraints.IMap` for the next release...)
Merge branch 'master' of github.com:misprintt/mockatoo into fix/#40-imap
Issue #40 - Added tests for maps
Merge pull request #41 from misprintt/origin/master

Issue #40