Make Travis work

[DavidLeoni]

Make Travis build also dependencies like evoscratch-vm

See Publishing-to-GitHub-Pages

In order to build, in .travis.yml you need to:

• add also prove whenever you see written develop
• disable npm caching
• disable npm deploy (if we enable it, we need to change all project ids which is too cumbersome for now)
• change Scratch wiki instructions so to insert && BUILD_MODE=dist npm run build && npm link in here:

install:
- npm --production=false install
- npm update
- cd node_modules/scratch-vm && ln -s $(npm root)/google-closure-library ../closure-library --force && npm --production=false install && BUILD_MODE=dist npm run build && npm link && cd -