Update bootstrap.js to fix browserify2:dev task

To fix error in task:

    Running "browserify2:dev" (browserify2) task
    >> Error: module "./bower_components/bootstrap/assets/js/holder" not found from "/path/to/yeoman-ultimate/client/js/node_modules/bootstrap.js"
    File written to: .tmp/js/main.js
Merge pull request #62 from hal-gh/dev

Fixed bootstrap assets path to fix browserify2:dev Grunt task.