Adding is_disabled option

[cheyner]

[cheyner]

The underlying Analytics package will simply return a NullResponse when prompted to send events to GA if the argument $isDisabled=true in its constructor. Ideally I would have included a test here, but there didn't appear to be a simple way to check that -- and it seemed like a fairly benign adjustment to me.

[kyranb]

@pascalbaljet Can we help merge this in?

[cheyner]

Checking in on this...

[sebastiaanluca]

👋 Was looking for a way to disable the package during tests. Currently it sends a ton of requests to Google 😬

[pascalbaljet]

I've changed it to is_enabled. Available in v1.5.1 :)