add new youtubedl dependency

downloader/vendor/github.com/kkdai/youtube/v2/decipher_operations.go

@@ -0,0 +1,27 @@
+package youtube
+
+type DecipherOperation func([]byte) []byte
+
+func newSpliceFunc(pos int) DecipherOperation {
+	return func(bs []byte) []byte {
+		return bs[pos:]
+	}
+}
+
+func newSwapFunc(arg int) DecipherOperation {
+	return func(bs []byte) []byte {
+		pos := arg % len(bs)
+		bs[0], bs[pos] = bs[pos], bs[0]
+		return bs
+	}
+}
+
+func reverseFunc(bs []byte) []byte {
+	l, r := 0, len(bs)-1
+	for l < r {
+		bs[l], bs[r] = bs[r], bs[l]
+		l++
+		r--
+	}
+	return bs
+}