refactor!: migrate to urfave/cli v1

Better flexible flags handling.

cli/server/server.go

@@ -1,11 +1,11 @@
 package server
 
 import (
-	"github.com/urfave/cli/v2"
+	"github.com/urfave/cli"
 )
 
 // ServerCommand defines the `abra server` command and its subcommands
-var ServerCommand = &cli.Command{
+var ServerCommand = cli.Command{
 	Name:    "server",
 	Aliases: []string{"s"},
 	Usage:   "Manage servers",
@@ -18,7 +18,7 @@ already have a server, you can add it to your configuration using "abra server
 add". Abra can provision servers so that they are ready to deploy Co-op Cloud
 apps, see available flags on "server add" for more.
 `,
-	Subcommands: []*cli.Command{
+	Subcommands: []cli.Command{
 		serverNewCommand,
 		serverAddCommand,
 		serverListCommand,