Filter unrenderable children

[DarkoKukovec]

In the current version only null is removed from children, but in order to keep compatibility with React, undefined, true and false should also be removed.

[DarkoKukovec]

I see that the tests have failed, but I'm not sure why (I can't reproduce it locally). There is something confusiong going on:

• CSSTransitionGroup transitionEnter works failed with error AssertionError: expected [ Array(5) ] to have a length of 3 but got 5, but this assertion is not done in this test.
• CSSTransitionGroup: SVG - not sure if the failed test is related to the change, also in the list of tests, it's marked as passing, but CSSTransitionGroup: NullChildren transitionEnter works is marked as failing

The issues seem to be some kind of race condition in the tests.
Any hints to what's going on and what I can do to fix it?