实训关卡的超时时间默认设置成20

db/migrate/20190629060410_change_exec_time_default_for_challenges.rb

@@ -0,0 +1,8 @@
+class ChangeExecTimeDefaultForChallenges < ActiveRecord::Migration
+  def up
+    change_column :challenges, :exec_time, :integer, :default => 20
+  end
+
+  def down
+  end
+end