npm总是报错,不能下载东西，错误如下图所示，请问大家如何解决

[zhendunkai6885]

npm ERR! fetch failed http://r.cnpmjs.org/mysql/download/mysql-2.13.0.tgz
npm WARN retry will retry, error on last attempt: Error: unable to verify the first certificate
npm ERR! fetch failed http://r.cnpmjs.org/mysql/download/mysql-2.13.0.tgz
npm WARN retry will retry, error on last attempt: Error: unable to verify the first certificate
npm ERR! fetch failed http://r.cnpmjs.org/mysql/download/mysql-2.13.0.tgz
npm ERR! Windows_NT 6.1.7601
npm ERR! argv "C:\\Program Files\\nodejs\\node.exe" "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "install" "mysql"
npm ERR! node v6.11.0
npm ERR! npm v3.10.10
npm ERR! code UNABLE_TO_VERIFY_LEAF_SIGNATURE

npm ERR! unable to verify the first certificate
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR! <https://github.com/npm/npm/issues>

npm ERR! Please include the following file with any support request:
npm ERR! F:\nodework\demo\day5\npm-debug.log