add test for lifting a lambda impl of filter
add test for lifting a lambda impl of filter

Reactive-Extensions/RxCpp,alexeymarkov/RxCpp,Reactive-Extensions/RxCpp,ReactiveX/RxCpp,alexeymarkov/RxCpp,ReactiveX/RxCpp,alexeymarkov/RxCpp,Reactive-Extensions/RxCpp,ReactiveX/RxCpp