fix Object.assign regression in JSXOpeningElement
Fixes #163 (closed)
Before fix:
$ echo '<MyThing two={"This Fails"} {...props}></MyThing>;' | bin/buble --objectAssign
React.createElement( MyThing, undefined({}, { two: "This Fails" }, props));
After fix:
$ echo '<MyThing two={"This no longer Fails"} {...props}></MyThing>;' | bin/buble --objectAssign
React.createElement( MyThing, Object.assign({}, { two: "This no longer Fails" }, props));