Update gulpfile.js and package.json

Dependencies were updated
Deprecated use was removed in gulp
Refactor tests, make them green!

Now use two modes for each tests with a function, instead of repeating the same test twice
Imrpovements for index.js

Return when we can, safer and we can prevent some indent.
Merge branch 'gulpfile-improvements'
Merge branch 'refactor-tests'