gulp build error: Libsass bindings not found

After setup, running gulp build for the first time gave me this error.

```
❯ gulp build
[22:28:06] Warning: gulp version mismatch:
[22:28:06] Global gulp is 3.9.1
[22:28:06] Local gulp is 3.8.11
[22:28:07] Using gulpfile ~/Vagrant/www/dalbey/htdocs/wp-content/themes/picard/gulpfile.js
[22:28:07] Starting 'styles'...
[22:28:07] 'styles' errored after 43 ms
[22:28:07] Error: `libsass` bindings not found. Try reinstalling `node-sass`?
```

Node v6.9.4
Mac OS Sierra

Reproduce the failure with `gulp build` using the reported Node v6.9.4 and inspect `gulpfile.js`, especially the `styles` task and its node-sass or Libsass dependency. Done means the styles task completes without the Libsass bindings error; the payload does not identify a test.

Written by the indexing model from the issue text.