Fix the error thrown by generating the gruntfile

[sondr3]

undefined:8
((__t = ( _.slugify(projectname) )) == null ? '' : __t) +
                    ^
ReferenceError: projectname is not defined
    at eval (/lodash/template/source[1]:8:21)
    at PlaybookGenerator.underscore [as _engine] (/home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/lib/util/engines.js:33:30)
    at PlaybookGenerator.engine (/home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/lib/actions/actions.js:291:10)
    at PlaybookGenerator.template (/home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/lib/actions/actions.js:269:15)
    at PlaybookGenerator.packageJSON (/home/sondre/Projects/generator-jekyllized/app/index.js:382:8)
    at /home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/lib/base.js:290:20
    at /home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/node_modules/async/lib/async.js:551:21
    at /home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/node_modules/async/lib/async.js:227:13
    at iterate (/home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/node_modules/async/lib/async.js:134:13)
    at /home/sondre/Projects/generator-jekyllized/node_modules/yeoman-generator/node_modules/async/lib/async.js:145:25