Update npm dependencies

[pioug]

chalk               1.1.3  ❯  2.4.1  https://github.com/chalk/chalk#readme
plugin-error        0.1.2  ❯  1.0.1  https://github.com/gulpjs/plugin-error#readme
through2            0.4.2  ❯  2.0.3  https://github.com/rvagg/through2#readme
gulp-jshint devDep  1.5.6  ❯  2.1.0  http://github.com/spalger/gulp-jshint
gulp-mocha devDep   2.2.0  ❯  6.0.0  https://github.com/sindresorhus/gulp-mocha#readme
mocha devDep        2.2.5  ❯  5.2.0  https://mochajs.org