Add default export to definition file

When using the `style-loader`, the `locals` object gets invisibly murdered. Fixes Jimdo/typings-for-css-modules-loader#20. If someone's not using the `style-loader` they can `import {locals}`, and if they _are_ using the `style-loader`, they can use the default import. This should make everyone happy, and be fully backwards-compatible.

Author: sarink

src/cssModuleToInterface.js

@@ -95,5 +95,6 @@ ${interfaceProperties}
 }
 
 export const locals: ${interfaceName};
+export default locals;
 `);
 };