Address error in README.

[karajan1001]

  import oss2

   auth = oss2.Auth('AccessKeySecret', 'AccessKeySecret')
   bucket = oss2.Bucket(auth, 'http//:192.168.0.1:8080', 'MyBucketName')
   bucket.create_bucket()

http//:192.168.0.1 -> http://192.168.0.1