Handle single child when using React inlining

Changes optimisation.react.inlineElements to handle a single child as the
value of the `children` property instead of wrapping it with an array.
This matches the behavior of `React.createElement`.

test/core/fixtures/transformation/optimisation.react.constant-elements/inline-elements/expected.js

@@ -16,11 +16,11 @@ function render() {
     type: "foo",
     ref: null,
     props: {
-      children: [text]
+      children: text
     },
     key: null
   };
   return function () {
     return _ref2;
   };
-}
+}