Fixup Redis lock context compilation error

Related to RichardKnop#793; see RichardKnop#803.

Author: agcom

v2/locks/redis/redis.go

@@ -64,7 +64,8 @@ func (r Lock) LockWithRetries(key string, unixTsToExpireNs int64) error {
 func (r Lock) Lock(key string, unixTsToExpireNs int64) error {
 	now := time.Now().UnixNano()
 	expiration := time.Duration(unixTsToExpireNs + 1 - now)
-	ctx := r.rclient.Context()
+	// ctx := r.rclient.Context()
+	ctx := context.Background()
 
 	success, err := r.rclient.SetNX(ctx, key, unixTsToExpireNs, expiration).Result()
 	if err != nil {