skip if RUBY_DEBUG_ENABLE=0

fix #730

Author: ko1

lib/debug.rb

@@ -1,4 +1,5 @@
 # frozen_string_literal: true
 
 require_relative 'debug/session'
+return unless defined?(DEBUGGER__)
 DEBUGGER__::start no_sigint_hook: true, nonstop: true

lib/debug/prelude.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+return if ENV['RUBY_DEBUG_ENABLE'] == '0'
 return if defined?(::DEBUGGER__)
 
 # Put the following line in your login script (e.g. ~/.bash_profile) with modified path: