address all races detected by by go race detector

[sduchesneau]

One of these may be related to #31

Starting dfuse for EOSIO with config file './dfuse.yaml'
Launching applications: abicodec,apiproxy,blockmeta,dashboard,dgraphql,eosq,eosws,fluxdb,merger,mindreader,node-manager,relayer,search-archive,search-indexer,search-live,search-router,trxdb-loader
==================
WARNING: DATA RACE
Write at 0x00c0004815d0 by goroutine 110:
  github.com/grpc-ecosystem/go-grpc-prometheus.WithHistogramBuckets.func1()
      /home/stepd/go/pkg/mod/github.com/grpc-ecosystem/[email protected]/metric_options.go:32 +0x6c
  github.com/grpc-ecosystem/go-grpc-prometheus.(*ServerMetrics).EnableHandlingTimeHistogram()
      /home/stepd/go/pkg/mod/github.com/grpc-ecosystem/[email protected]/server_metrics.go:65 +0x91
  github.com/grpc-ecosystem/go-grpc-prometheus.EnableHandlingTimeHistogram()
      /home/stepd/go/pkg/mod/github.com/grpc-ecosystem/[email protected]/server.go:46 +0x6c
  github.com/dfuse-io/dgrpc.NewServer()
      /home/stepd/go/pkg/mod/github.com/dfuse-io/[email protected]/server.go:141 +0xb52
  github.com/dfuse-io/dfuse-eosio/dashboard.(*server).Launch()
      /home/stepd/repos/dfuse-eosio/dashboard/server.go:75 +0x1c4
  github.com/dfuse-io/dfuse-eosio/dashboard.(*App).Run.func1()
      /home/stepd/repos/dfuse-eosio/dashboard/app.go:66 +0x3c
...

(see more attached)

[sduchesneau]

races-log.txt