install with yarn in the build script
This seems to make the project build for me, when I remove output/ and node_modules/
i.e.
$ rm -rf output node_modules/
$ build
[ ... a bunch of things happen ]
$ /home/justin/Code/purescript-gargantext/node_modules/.bin/pulp browserify --skip-compile -t dist/bundle.js --src-path output
* Browserifying project in /home/justin/Code/purescript-gargantext
* Browserifying...
* Browserified.
Done in 4.09s.