handle parenthesised default exports (#136)

src/Module.js

@@ -495,7 +495,8 @@ export default class Module {
 				ast = parse( this.source, {
 					ecmaVersion: 6,
 					sourceType: 'module',
-					onComment: ( block, text, start, end ) => this.comments.push({ block, text, start, end })
+					onComment: ( block, text, start, end ) => this.comments.push({ block, text, start, end }),
+					preserveParens: true
 				});
 			} catch ( err ) {
 				err.code = 'PARSE_ERROR';

test/function/parenthesised-default-export/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'allows default exports to be enclosed in parentheses'
+};

test/function/parenthesised-default-export/main.js

@@ -0,0 +1 @@
+export default ( 42 );