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`.

src/babel/transformation/transformers/optimisation/react.inline-elements.js

@@ -49,7 +49,9 @@ export var visitor = {
     pushElemProp("ref", t.literal(null));
 
     if (node.children.length) {
-      pushProp(props.properties, t.identifier("children"), t.arrayExpression(react.buildChildren(node)));
+      var children = react.buildChildren(node);
+      children = children.length === 1 ? children[0] : t.arrayExpression(children);
+      pushProp(props.properties, t.identifier("children"), children);
     }
 
     // props