Update go dependencies (#4322)

vendor/github.com/gregjones/httpcache/.travis.yml

@@ -4,7 +4,6 @@ go:
   - 1.6.x
   - 1.7.x
   - 1.8.x
-  - 1.9.x
   - master
 matrix:
   allow_failures:

vendor/github.com/gregjones/httpcache/README.md

@@ -3,7 +3,7 @@ httpcache
 
 [![Build Status](https://travis-ci.org/gregjones/httpcache.svg?branch=master)](https://travis-ci.org/gregjones/httpcache) [![GoDoc](https://godoc.org/github.com/gregjones/httpcache?status.svg)](https://godoc.org/github.com/gregjones/httpcache)
 
-Package httpcache provides a http.RoundTripper implementation that works as a mostly [RFC 7234](https://tools.ietf.org/html/rfc7234) compliant cache for http responses.
+Package httpcache provides a http.RoundTripper implementation that works as a mostly RFC-compliant cache for http responses.
 
 It is only suitable for use as a 'private' cache (i.e. for a web-browser or an API-client and not for a shared proxy).
 
@@ -17,7 +17,6 @@ Cache Backends
 - [`github.com/gregjones/httpcache/leveldbcache`](https://github.com/gregjones/httpcache/tree/master/leveldbcache) provides a filesystem-backed cache using [leveldb](https://github.com/syndtr/goleveldb/leveldb).
 - [`github.com/die-net/lrucache`](https://github.com/die-net/lrucache) provides an in-memory cache that will evict least-recently used entries.
 - [`github.com/die-net/lrucache/twotier`](https://github.com/die-net/lrucache/tree/master/twotier) allows caches to be combined, for example to use lrucache above with a persistent disk-cache.
-- [`github.com/birkelund/boltdbcache`](https://github.com/birkelund/boltdbcache) provides a BoltDB implementation (based on the [bbolt](https://github.com/coreos/bbolt) fork).
 
 License
 -------

vendor/github.com/gregjones/httpcache/httpcache.go

@@ -10,6 +10,7 @@ import (
 	"bufio"
 	"bytes"
 	"errors"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -40,11 +41,7 @@ type Cache interface {
 
 // cacheKey returns the cache key for req.
 func cacheKey(req *http.Request) string {
-	if req.Method == http.MethodGet {
-		return req.URL.String()
-	} else {
-		return req.Method + " " + req.URL.String()
-	}
+	return req.URL.String()
 }
 
 // CachedResponse returns the cached http.Response for req if present, and nil
@@ -192,11 +189,16 @@ func (t *Transport) RoundTrip(req *http.Request) (resp *http.Response, err error
 			for _, header := range endToEndHeaders {
 				cachedResp.Header[header] = resp.Header[header]
 			}
+			cachedResp.Status = fmt.Sprintf("%d %s", http.StatusOK, http.StatusText(http.StatusOK))
+			cachedResp.StatusCode = http.StatusOK
+
 			resp = cachedResp
 		} else if (err != nil || (cachedResp != nil && resp.StatusCode >= 500)) &&
 			req.Method == "GET" && canStaleOnError(cachedResp.Header, req.Header) {
 			// In case of transport failure and stale-if-error activated, returns cached content
 			// when available
+			cachedResp.Status = fmt.Sprintf("%d %s", http.StatusOK, http.StatusText(http.StatusOK))
+			cachedResp.StatusCode = http.StatusOK
 			return cachedResp, nil
 		} else {
 			if err != nil || resp.StatusCode != http.StatusOK {