Update dependencies to K8s 1.8

vendor/github.com/google/btree/README.md

@@ -0,0 +1,12 @@
+# BTree implementation for Go
+
+![Travis CI Build Status](https://api.travis-ci.org/google/btree.svg?branch=master)
+
+This package provides an in-memory B-Tree implementation for Go, useful as
+an ordered, mutable data structure.
+
+The API is based off of the wonderful
+http://godoc.org/github.com/petar/GoLLRB/llrb, and is meant to allow btree to
+act as a drop-in replacement for gollrb trees.
+
+See http://godoc.org/github.com/google/btree for documentation.