Avoid error when state.children is a function call (CallExpression)

[leonid-shevtsov]

I encountered an error when the value of a children property was a function call, not an array.

Specific example:

children: angular.copy(initialStateArrayThatIsReused)

I'm not experienced with Babel enough to explain why this happens - getting elements seems reliable enough to me. But, adding an explicit check that children is an array makes the problem go away.

I'm using Babel version 6.26.0.