Use cleanhttp instead of bare http.Client

builtin/credential/github/backend.go

@@ -1,9 +1,8 @@
 package github
 
 import (
-	"net/http"
-
 	"github.com/google/go-github/github"
+	"github.com/hashicorp/go-cleanhttp"
 	"github.com/hashicorp/vault/logical"
 	"github.com/hashicorp/vault/logical/framework"
 	"golang.org/x/oauth2"
@@ -54,7 +53,7 @@ type backend struct {
 // Client returns the GitHub client to communicate to GitHub via the
 // configured settings.
 func (b *backend) Client(token string) (*github.Client, error) {
-	tc := &http.Client{}
+	tc := cleanhttp.DefaultClient()
 	if token != "" {
 		tc = oauth2.NewClient(oauth2.NoContext, &tokenSource{Value: token})
 	}