Switch from eth/66 to eth/67

DEV_CHAIN.md

README.md

cmd/observer/observer/handshake.go

cmd/observer/observer/handshake_test.go

cmd/observer/observer/sentry_candidates/log_test.go

cmd/observer/observer/server.go

cmd/sentry/main.go

cmd/sentry/sentry/broadcast.go

cmd/sentry/sentry/eth_handshake_test.go

cmd/sentry/sentry/sentry_api.go

cmd/sentry/sentry/sentry_grpc_server.go

cmd/sentry/sentry/sentry_grpc_server_test.go

cmd/sentry/sentry/sentry_multi_client.go

cmd/utils/flags.go

eth/backend.go

eth/protocols/eth/handler_test.go

eth/protocols/eth/protocol.go

eth/protocols/eth/protocol_test.go

ethdb/privateapi/ethbackend.go

p2p/dial_test.go