gometalinter -> golangci-lint migration (#3933)

{,scripts/}Makefile:
- Remove gometalinter, install golangci-lint.
- Remove distinction between tools and devtools.
  Just tools is enough.
- test_lint -> lint
  Migrating away from underscore separated names.
- Remove unnecessary targets.
- Drop tendermint/lint. Incompatbile with golangci-lint
  and no longer necessary anyway.
- Fix misleading message in go-mod-cache.
- New ci-target to avoid download tools twice.
- Run tests with -mod=readonly.

Port tools/gometalinter.json to .golangci.yml
Update CircleCI config accordingly.

Closes: #3896

client/rest/rest.go

@@ -1,6 +1,7 @@
 package rest
 
 import (
+	"log"
 	"net/http"
 
 	"github.com/cosmos/cosmos-sdk/client"
@@ -67,6 +68,8 @@ func WriteGenerateStdTxResponse(w http.ResponseWriter, cdc *codec.Codec,
 	}
 
 	w.Header().Set("Content-Type", "application/json")
-	w.Write(output)
+	if _, err := w.Write(output); err != nil {
+		log.Printf("could not write response: %v", err)
+	}
 	return
 }