And it isn’t some weird Travis-CI thing either (like the cache they enabled by default for npm this July) because it doesn’t work here either (pinned that down to sync-request by the way).
Well, I found the problem (it was on my end). Both 75a57ad and 92eaaf5 in the sync-rpc sub-dependency break, on their own, Node 6 support. And it was in a patch-level version bump on, so I didn’t notice the difference.