ADD repositories表中添加fork_url字段

db/migrate/20200515024117_add_fork_url_to_repositories.rb

@@ -0,0 +1,5 @@
+class AddForkUrlToRepositories < ActiveRecord::Migration[5.2]
+  def change
+    add_column :repositories, :fork_url, :string, default: nil
+  end
+end