vendor: update buildkit to opentelemetry support

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/google.golang.org/appengine/.travis.yml

@@ -10,6 +10,8 @@ script:
 
 matrix:
   include:
+    - go: 1.8.x
+      env: GOAPP=true
     - go: 1.9.x
       env: GOAPP=true
     - go: 1.10.x

vendor/google.golang.org/appengine/internal/api.go

@@ -58,11 +58,8 @@ var (
 
 	apiHTTPClient = &http.Client{
 		Transport: &http.Transport{
-			Proxy:               http.ProxyFromEnvironment,
-			Dial:                limitDial,
-			MaxIdleConns:        1000,
-			MaxIdleConnsPerHost: 10000,
-			IdleConnTimeout:     90 * time.Second,
+			Proxy: http.ProxyFromEnvironment,
+			Dial:  limitDial,
 		},
 	}