Allow presets to be ES6 exports.

packages/babel-core/src/transformation/file/options/option-manager.js

@@ -281,6 +281,9 @@ export default class OptionManager {
           val = require(presetLoc);
         }
 
+        // If the imported preset is a transpiled ES2015 module, grab the default export.
+        if (typeof val === "object" && val.__esModule) val = val.default;
+
         // For compatibility with babel-core < 6.13.x, allow presets to export an object with a
         // a 'buildPreset' function that will return the preset itself, while still exporting a
         // simple object (rather than a function), for supporting old Babel versions.