由于文件锁定，为什么在npm安装期间TravisCI构建失败

Question

由于文件锁定问题，

npm install失败。我怎么能避免这个？

Here is the log of travis-ci：

npm ERR! EEXIST, open '/home/travis/.npm/83f1dfb7-vis-npm-lodash-2-4-1-package-tgz.lock'
File exists: /home/travis/.npm/83f1dfb7-vis-npm-lodash-2-4-1-package-tgz.lock
Move it away, and try again. 
npm ERR! System Linux 2.6.32-042stab090.5
npm ERR! command "/home/travis/.nvm/v0.10.32/bin/node" "/home/travis/.nvm/v0.10.32/bin/npm" "install"
npm ERR! cwd /home/travis/build/wordnik/swagger-editor
npm ERR! node -v v0.10.32
npm ERR! npm -v 1.4.28
npm ERR! path /home/travis/.npm/83f1dfb7-vis-npm-lodash-2-4-1-package-tgz.lock
npm ERR! code EEXIST
npm ERR! errno 47
npm ERR! not ok code 0
The command "npm install" failed and exited with 47 during .

Answer 1

更新到npm到版本2解决了我的问题。

install:
  - npm install -g npm@2