use loose model for es6 classes

test/test.js

@@ -94,7 +94,8 @@ describe( 'rollup', function () {
 						try {
 							if ( config.babel ) {
 								code = babel.transform( result.code, {
-									blacklist: [ 'es6.modules' ]
+									blacklist: [ 'es6.modules' ],
+									loose: [ 'es6.classes' ]
 								}).code;
 							} else {
 								code = result.code;
@@ -262,7 +263,8 @@ describe( 'rollup', function () {
 							try {
 								if ( config.babel ) {
 									code = babel.transform( code, {
-										blacklist: [ 'es6.modules' ]
+										blacklist: [ 'es6.modules' ],
+										loose: [ 'es6.classes' ]
 									}).code;
 								}