chore(package.json): update devDependencies

grunt-contrib-clean v0.5.0 -> v0.6.0
grunt-contrib-concat v0.4.0 -> v0.5.0
grunt-contrib-connect v0.7.1 -> v0.8.0
grunt-contrib-uglify v0.4.0 -> v0.5.1
semver v2.3.0 -> v3.0.0

Closes #29