Add support for GTMSessionFetcher 2.x

[paulb777]

Firebase's next major version update will require GTMSessionFetcher 2.1 and that's incompatible with the current GTMAppAuth dependency.

Is it possible to support both 1.x and 2.x as dependencies?

Firebase had previously been supporting both via this podspec specification:

s.dependency 'GTMSessionFetcher/Core', '>= 1.7', '< 3.0'

Integration test failure here : https://github.com/firebase/firebase-ios-sdk/runs/7927314766?check_suite_focus=true#step:6:169

[paulb777]

Looks like this was implemented in #155 and awaiting the 1.3.1 release.

[petea]

Yes, we can ship 1.3.1 shortly if needed.

Is there a timeline for the next Firebase major release? We'll probably want to update GSI's GTMSessionFetcher dependency too.

[mdmathias]

@petea can this issue be closed?

[petea]

@petea can this issue be closed?

Yes, this was addressed in 1.3.1.