v4.0.0

FANFOU-SDK 4.0 🎉

Here are the changes of fanfou-sdk 4:

• Remove fakeHttps option
• Drop support for Node.js 4
• Remove built-in sign name module
• Use got instead of request
• Use oauth-1.0a instead of oauth
• Completely async/await
• Throw error on non-200 HTTP status code cases
• Merge ff.upload() to ff.post()
• Update tests