Fix plugin order to re-enable using decorators (codesandbox#154)

For example https://codesandbox.io/s/2vmzpM0wK is now broken. See also: mobxjs/mobx#1154

Fixes codesandbox#151

Author: mweststrate

src/sandbox/eval/transpilers/babel/babel-parser.js

@@ -8,8 +8,8 @@ const DEFAULT_BABEL_CONFIG = {
   plugins: [
     'transform-async-to-generator',
     'transform-object-rest-spread',
-    'transform-class-properties',
     'transform-decorators-legacy',
+    'transform-class-properties',
   ],
 };