Update vendor

vendor/github.com/valyala/bytebufferpool/doc.go

@@ -0,0 +1,7 @@
+// Package bytebufferpool implements a pool of byte buffers
+// with anti-fragmentation protection.
+//
+// The pool may waste limited amount of memory due to fragmentation.
+// This amount equals to the maximum total size of the byte buffers
+// in concurrent use.
+package bytebufferpool