Rollback `handle` to `weixin`: postpone renaming them in v2.0.0

[huan]

According to the report from

• https://github.com/wechaty/getting-started/issues/254

We realized that the npm package dependency of wechaty-grpc@^1.0.0 will automatically install the latest v1.x version, which will introduce breaking change to the existing ecosystem.

So we have to roll the changes back and plan to rename weixin to handle in v2.0.0

Related to:

• https://github.com/wechaty/grpc/pull/173