LookupIn operations raise PathNotFound instead of PathMismatch errors when count is requested on a path that is not an array

For example,

collection.upsert('test',{:foo=>10, :bar=>{:nested => 11}})

res = collection.lookup_in('test', [LookupInSpec.count('foo')])

res.content(0)

The last line should raise a PathMismatch error, it raises PathNotFound instead

The following failing FIT test should pass after this is fixed:
 * pathMismatchCountLookup