capistrano: fix git deprecation warning.

Capfile

@@ -4,6 +4,9 @@ require 'capistrano/setup'
 # Include default deployment tasks
 require 'capistrano/deploy'
 
+require "capistrano/scm/git"
+install_plugin Capistrano::SCM::Git
+
 # Include tasks from other gems included in your Gemfile
 require 'capistrano/rbenv'
 require 'capistrano/rails'

config/deploy.rb

@@ -2,7 +2,6 @@ set :stages, %w(production development staging)
 set :default_stage, "staging"
 set :application, "danbooru"
 set :repo_url,  "git://github.com/r888888888/danbooru.git"
-set :scm, :git
 set :deploy_to, "/var/www/danbooru2"
 set :rbenv_ruby, "2.5.1"
 set :linked_dirs, fetch(:linked_dirs, []).push('log', 'tmp/pids', 'tmp/cache', 'tmp/sockets', 'vendor/bundle')