build: make protobuf requires internet access

[a-robinson]

It's hardly the end of the world, but is there an easy way to make building our protocol buffers not require internet access? If I change a proto (e.g. by adding a new enum value to storage/log.proto) and try to run make protobuf without being connected to the internet, it always hangs on an npm command:

⸨░░░░░░░░░░░░░░░░░░⸩ ⠧ normalizeTree: sill install loadCurrentTree

I also got it hung in this other place once when I disconnected from the internet while make protobuf was in the middle of running:

⸨    ░░░░░░░░░░░░░░⸩ ⠴ fetchMetadata: sill mapToRegistry uri https://registry.npmjs.org/taffydb
⸨    ░░░░░░░░░░░░░░⸩ ⠇ fetchMetadata: verb afterAdd /Users/alex/.npm/marked/0.3.6/package/package.json written

Connecting to the internet fixes things. I don't remember it having always been this way.

cc @cockroachdb/build

[benesch]

I'm pretty sure this is due to a bug in protobuf.js (protobufjs/protobuf.js#716). We very intentionally run yarn install, which will avoid hitting the network if all deps are satisfied, but pbjs runs npm install behind our back, which I assume hits the network for something. It's pretty terrible.

[a-robinson]

This works for me now.