func ContextWithTxn(c context.Context, txn newrelic.Transaction) context.Context {
	return context.WithValue(c, txnKey, txn)
}
Set NewRelic transaction to context
package nrcontext
import (
	"context"
	"github.com/jinzhu/gorm"
	"github.com/newrelic/go-agent"
	"github.com/smacker/newrelic-context/nrgorm"
	"github.com/smacker/newrelic-context/nrredis"
	redis "gopkg.in/redis.v5"
)
type contextKey int
const txnKey contextKey = 0