undefined method `environment' for nil:NilClass when importing Bootstrap into rails

今天做项目时往Gemfile里加了各gem，　然后bundle update了一下，　然后悲剧了，出现了undefined method `environment' for nil:NilClass when importing Bootstrap into rails错误，　各种不理解．　然后查了一下，　找到了解决方案:

https://stackoverflow.com/questions/22392862/undefined-method-environment-for-nilnilclass-when-importing-bootstrap