Update PlatformIO registry

[hpsaturn]

Thanks for resolve the issue #9. I tested with the last master branch and works fine, but the PlatformIO publication is outdated:

https://registry.platformio.org/libraries/phzi/DFRobot_MultiGasSensor

Please populate the current master to the Pio registry. Thanks!

[96liuzhixin]

We hit the new tag package V3.0.0
And we don't know how to deal with the synchronization of PlatformIO that has been uploaded.

[hpsaturn]

Well, is easy. You only need an manifest and publish the library like this:
https://docs.platformio.org/en/latest/librarymanager/creating.html