[gist] Use first configured API hosts instead of prompting

If hub is configured with multiple hosts (usually including GitHub
Enterprise instances), every invocation to `hub gist` would prompt to
select a host. Assume that people want to use the first configured host
by default (they can change it via GITHUB_HOST).

commands/gist.go

@@ -114,7 +114,7 @@ func printGistHelp(command *Command, args *Args) {
 func createGist(cmd *Command, args *Args) {
 	args.NoForward()
 
-	host, err := github.CurrentConfig().DefaultHost()
+	host, err := github.CurrentConfig().DefaultHostNoPrompt()
 	utils.Check(err)
 	gh := github.NewClient(host.Host)
 
@@ -132,7 +132,7 @@ func createGist(cmd *Command, args *Args) {
 func showGist(cmd *Command, args *Args) {
 	args.NoForward()
 
-	host, err := github.CurrentConfig().DefaultHost()
+	host, err := github.CurrentConfig().DefaultHostNoPrompt()
 	utils.Check(err)
 	gh := github.NewClient(host.Host)