yo bootstrap

hinmn-mbp:bootstrap hinmn$ yo bootstrap
In what format would you like the Twitter Bootstrap stylesheets? (css/sass/less) sass

/Users/hinmn/node_modules/generator-bootstrap/app/index.js:50
  this.install(packages[this.format]);
       ^
TypeError: Object #<Generator> has no method 'install'
    at Generator.bootstrapFiles (/Users/hinmn/node_modules/generator-bootstrap/app/index.js:50:8)
    at next (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/lib/base.js:275:18)
    at Base.run.self.async (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/lib/base.js:267:11)
    at next (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/lib/util/conflicter.js:52:14)
    at EventEmitter.resolve (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/lib/util/conflicter.js:64:5)
    at Base.run.self.async (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/lib/base.js:262:20)
    at Generator.askFor (/Users/hinmn/node_modules/generator-bootstrap/app/index.js:37:5)
    at next (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/lib/actions/prompt.js:21:14)
    at prompt.prompt (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/lib/actions/prompt.js:33:7)
    at Interface.onLine (/Users/hinmn/node_modules/generator-bootstrap/node_modules/yeoman-generator/node_modules/read/lib/read.js:110:5)