【node-pre-gyp install --fallback-to-build 错误】
npm install bcrypt时遇上错误
此时，安装node-gyp
npm install -g node-gyp然后，再安装bcrypt即可。
【node-gyp】
Node.js native addon build tool
node-gyp is a cross-platform command-line tool written in Node.js for compiling native addon modules for Node.js. It bundles the gyp project used by the Chromium team and takes away the pain of dealing with the various differences in build platforms.
node-gyp用于将工具源码编译成ndoejs add-on
参考：
