Update vendor (slack)

vendor/github.com/nlopes/slack/examples/groups/groups.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/nlopes/slack"
+)
+
+func main() {
+	api := slack.New("YOUR_TOKEN_HERE")
+	// If you set debugging, it will log all requests to the console
+	// Useful when encountering issues
+	// api.SetDebug(true)
+	groups, err := api.GetGroups(false)
+	if err != nil {
+		fmt.Printf("%s\n", err)
+		return
+	}
+	for _, group := range groups {
+		fmt.Printf("ID: %s, Name: %s\n", group.ID, group.Name)
+	}
+}