Rails服务器无法启动。：undefined局部变量或方法`config＆＃39; for main：对象

Question

尝试加载rails服务器时收到以下错误：

/config/environments/development.rb:55:in '<top (required)>': undefined 
local variable or method 'config' for main:Object (NameError)

我不知道从哪里开始这个错误。任何帮助将不胜感激。

的Gemfile：

source 'https://rubygems.org'
    ruby "2.4.1"
    git_source(:github) do |repo_name|
    repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
    "https://github.com/#{repo_name}.git"
    end
    gem 'rails', '5.2.0.rc1'
    gem 'puma', '~> 3.7'
    gem 'sass-rails', '~> 5.0'
    gem 'uglifier', '>= 1.3.0'
    gem 'jquery-rails'
    gem 'coffee-rails', '~> 4.2'
    gem 'turbolinks', '~> 5'
    gem 'jbuilder', '~> 2.5'

    gem 'bootstrap', '~> 4.0.0.alpha6'
    gem 'devise'

    group :development, :test do
    gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
    gem 'sqlite3'
    gem 'capybara', '~> 2.13'
    gem 'selenium-webdriver'
    end

    group :development do

    gem 'web-console', '>= 3.3.0'
    gem 'listen', '>= 3.0.5', '< 3.2'
    gem 'spring'
    gem 'spring-watcher-listen', '~> 2.0.0'
    end