fix golangci-lint failed (#284)

* fix golangci-lint error

cache/memory.go

@@ -62,13 +62,13 @@ func (mem *Memory) Set(key string, val interface{}, timeout time.Duration) (err
 
 //Delete delete value in memcache.
 func (mem *Memory) Delete(key string) error {
-	return mem.deleteKey(key)
+	mem.deleteKey(key)
+	return nil
 }
 
 // deleteKey
-func (mem *Memory) deleteKey(key string) error {
+func (mem *Memory) deleteKey(key string) {
 	mem.Lock()
 	defer mem.Unlock()
 	delete(mem.data, key)
-	return nil
 }

cache/redis.go

@@ -95,10 +95,7 @@ func (r *Redis) IsExist(key string) bool {
 
 	a, _ := conn.Do("EXISTS", key)
 	i := a.(int64)
-	if i > 0 {
-		return true
-	}
-	return false
+	return i > 0
 }
 
 //Delete 删除