Deploying the 8.4.0-snapshot on the Apache snapshot maven

[Sheng Wu]

Hi dev team

For the testing requirement, I run `mvn deploy` to upload the
8.4.0-snapshot to the snapshot maven repo. Matching the commit id[1].

[1]
https://github.com/apache/skywalking/tree/eb4b1215304dbab14a56b0916058b713192d5361

Sheng Wu 吴晟
Twitter, wusheng1108