Gem versioning

[rbngzlv]

I have doubts about the versioning / synchronization with core that uses this gem.

If we take as example the tag v1.2.0, it have the following line in their gemspec:

s.add_runtime_dependency 'solidus_core', ['>= 1.1', '< 3']

I'm not sure that this is correct. We can check this key as example:

spree.promotion_rule_types

• This key is not present in es.yml file, but is present in another locale files.
• This key is renamed in core since 2.3 version

Perhaps, we need to keep a set of branches in sync with core releases? Or use a external tool to stay in sync with the core changes and manage the translations?