add test for Crispy.spied?
I forgot assert_not is not defined
I got the wrong way to test `spied?`

spy_into doesn't return the spied object, but the spy for the spied object.
implement `spied?`

ask if the given object is spied by Crispy or not.

I need this API to hide __CRISPY_SPY__ from rspec-crispy.
add cases for BasicObject
Revert "add cases for BasicObject"

This reverts commit 77023333af833c71fdb39813d3175fd0322c58a0.

I decided not to support BasicObject with this API
Because we use BasicObject rarely alone.
Merge pull request #18 from igrep/predicates_spied

Add predicate method `spied?`