[Spec/Fixtures/SpecRepos/Master] Update
[Resolver] Scope dependencies in #edge_is_valid_for_target? by the spec's consume for that target's platform

This replaces the hack of `Dependency#from_subspec_dependency?`
[Documentation][Resolver] Remove references to #from_subspec_dependency? and talk instead about scoping by target platform
[Gemfile] Move back to Cores master
Merge pull request #2780 from CocoaPods/scope-dependencies-by-consumer

[Resolver] Scope dependencies in #edge_is_valid_for_target? by the spec's consume for that target's platform