This is a two part problem.
First part: "gulp-sass" is used in run-build.js but is not listed as a dependency in package.json.
Second part: Even after installing the gulp-sass module, I get the following error both during the module install and when trying to run the build script after installing the module. I'm on Mac OS X 10.10.3 (Yosemite)
dyld: lazy symbol binding failed: Symbol not found: __ZN2v86Object3SetENS_6HandleINS_5ValueEEES3_
Referenced from: /Users/kschultz/Git/Newell/visualizer-browser-client/node_modules/gulp-sass/node_modules/node-sass/vendor/darwin-x64-14/binding.node
Expected in: flat namespace
dyld: Symbol not found: __ZN2v86Object3SetENS_6HandleINS_5ValueEEES3_
Referenced from: /Users/kschultz/Git/Newell/visualizer-browser-client/node_modules/gulp-sass/node_modules/node-sass/vendor/darwin-x64-14/binding.node
Expected in: flat namespace