many fixes for lint and context.Context usage (#5)

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

client/client.go

@@ -9,6 +9,7 @@ import (
 )
 
 var (
+	// DefaultClient is the global default client
 	DefaultClient Client = NewClient()
 )
 

client/noop.go

@@ -4,9 +4,9 @@ import (
 	"context"
 
 	raw "github.com/unistack-org/micro-codec-bytes"
+	json "github.com/unistack-org/micro-codec-json"
 	"github.com/unistack-org/micro/v3/broker"
 	"github.com/unistack-org/micro/v3/codec"
-	"github.com/unistack-org/micro/v3/codec/json"
 	"github.com/unistack-org/micro/v3/errors"
 	"github.com/unistack-org/micro/v3/metadata"
 )