Your builds are failing with the following error message:
Node Sass could not find a binding for your current environment: Linux 64-bit
The rest of the error message in the build log may contain the following:
Found bindings for the following environments: - OS X 64-bit with Node.js 4.x This usually happens because your environment has changed since running `npm install`. Run `npm rebuild node-sass` to build the binding for your current environment.
This can occur when you have compiled modules locally and checked the resulting
node_modules folder into git before deploying. To fix this, we recommend removing the
node_modules folder from your git repo and redeploying.
You can find steps for this here: https://devcenter.heroku.com/articles/troubleshooting-node-deploys#don-t-check-in-generated-directories