为什么TravisCI在npm安装期间由于文件锁定而失败

Question

npm install由于文件锁定问题而失败。我怎样才能避免这种情况？

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版本2固定我的问题。

install: 
    - npm install -g npm@2