Don't enable emulators by default.

[luc122c]

After upgrading to the latest version, I got the following console warning:

Warning
You enabled emulators but there is no emulators key in your firebase.json file. Emulators will not be enabled.

This is in a project where I am not using the emulators. After taking a look through the code, I noticed that as of #1392, emulators are enabled by default.

Even though it is only a warning, I feel that since support for emulators is new enabling them by default is a breaking change. I'd suggest changing the default to false. I'd be more than happy to contribute a section on enabling emulator support to the vuefire docs.

[posva]

Emulators should be active only if they are defined in your firebase.json, it was a mistake that they were fully enabled by default but it should be fixed now! Thanks for reaching out!