Remove dependency in gulp

[lcampos]

Details

The project should not depend on gulp to build/deploy.

[ntotten]

Out of curiosity, why? I don't really care, just wondering.

[vazexqi]

I guess it's just one more dependency. If we don't need anything specific from gulp, it would be easier to just use npm run scripts. The other Salesforce DX projects (including the project generator) are just using plain npm scripts.

Also (might not be too representative), but see https://ashleynolan.co.uk/blog/frontend-tooling-survey-2018-results (Q13 – Task Runners) and see how the community is leaning toward npm scripts.

npm scripts can be made OS compatible using things like shelljs and cross-env. We use those in our vscode extensions.