Update package.js so simple-schema can support Meteor 0.6.5

I am using _collection2_ which depend on _simple-schema_, when upgrade to Meteor 0.6.5, collection2 has been broken because we must manually export what global variable we want. 

More info here
Follow up https://docs.meteor.com/#writingpackages

Fix here
```api.export(['SimpleSchema', 'SchemaRegEx'], ['client', 'server']);```