v0.2.50

Highlights:
Make simplification more robust when complexity limits are reached
reduces loop iteration counter to 6 before bailing out
We weren’t using the correct initializerAstNodeName in two places
Tease apart expressions vs. statements for operation descriptors
Simplify equality expressions where types are known
Refactor AbstractObjectValue to use evaluateWithAbstractConditional
Allow invalid render return values in the React reconciler
update Babel 7 to stable release
Speed up simplifier by using an implication cache per path branch
Add basic support for throws in React