Node Sass could not find a binding for your current environment: Linux 64-bit with Node.js 6.x

Found bindings for the following environments:
  - Linux 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.

最初Circle CIデフォルトの4系でbuildしててあとから6にしたせいだった。
Rebuild without cacheで解消した。