Fix initialization issue with access_token
Fix initialization issue with access_token

This resolves client initialization issue when specifying access_token
directly instead of giving api_key and api_secret to generate one. The
following line works now:
client = WeiboOAuth2::Client.from_hash(access_token: YOUR_TOKEN)

kediaco/weibo_2,santochan/weibo_2,simsicon/weibo_2