Metadata assumes it de-serializes to Symbol keys

[xxx]

I'm moving to use JSON as the serializer for our events, since JSON is far more universal outside of the Ruby world, but Metadata#[]= assumes keys will be Symbols, and raises an ArgumentError if not. This isn't the case with events that are dumped to and loaded from JSON. Here are a couple specs that demonstrate this:

      let(:yaml_store) do
        RailsEventStore::Client.new(
          dispatcher: RailsEventStore::ActiveJobDispatcher.new(
            proxy_strategy: RailsEventStore::AsyncProxyStrategy::AfterCommit.new
          )
        )
      end

      let(:json_store) do
        RailsEventStore::Client.new(
          mapper: RubyEventStore::Mappers::Default.new(
            serializer: JSON
          ),
          dispatcher: RailsEventStore::ActiveJobDispatcher.new(
            proxy_strategy: RailsEventStore::AsyncProxyStrategy::AfterCommit.new
          )
        )
      end

      let(:event) { RailsEventStore::Event.new(data: {}, metadata: {}) }

      # fails, but should pass
      it 'publishes JSON-serialized events without error' do
        event_store = json_store
        event_store.publish event
        expect(event_store).to have_published(an_event(RailsEventStore::Event))
      end

      # passes as expected
      it 'publishes YAML-serialized events without error' do
        event_store = yaml_store
        event_store.publish event
        expect(event_store).to have_published(an_event(RailsEventStore::Event))
      end

[mostlyobvious]

Related: #367

[xxx]

ah, duplicate. I couldn't find it for wahtever reason. Let's close this one.

[mostlyobvious]

No problem, I had this one in memory :)