Add a script for nodejs canary versions

We have something like the following copied into countless repos. It'd be nice if we could just grab it (or something similar) from here rather than rewriting it for every new project.

```js
#!/usr/bin/env node

const fs = require('fs')
const pkg = require('../client/package.json')

if (!process.env.CIRCLE_SHA1) {
throw new Error('No CIRCLE SHA available.')
}

const next = pkg.version + '-next.' + process.env.CIRCLE_SHA1.substring(0, 8)
pkg.version = next
fs.writeFileSync('./client/package.json', JSON.stringify(pkg, null, 2))
```