Rebuild node-sass after yarn install

[tnation14]

Overview

Occasionally, CI builds will fail becausenode-sass is missing the linux binding in the vendor directory:

ModuleBuildError: Module build failed: Error: ENOENT: no such file or directory, scandir '/opt/raster-foundry/app-frontend/node_modules/node-sass/vendor'
    at Error (native)
    at Object.fs.readdirSync (fs.js:951:18)
    at Object.getInstalledBinaries (/opt/raster-foundry/app-frontend/node_modules/node-sass/lib/extensions.js:121:13)
    at foundBinariesList (/opt/raster-foundry/app-frontend/node_modules/node-sass/lib/errors.js:20:15)
    at foundBinaries (/opt/raster-foundry/app-frontend/node_modules/node-sass/lib/errors.js:15:5)
    at Object.module.exports.missingBinary (/opt/raster-foundry/app-frontend/node_modules/node-sass/lib/errors.js:45:5)
    at module.exports (/opt/raster-foundry/app-frontend/node_modules/node-sass/lib/binding.js:15:30)
    at Object.<anonymous> (/opt/raster-foundry/app-frontend/node_modules/node-sass/lib/index.js:14:35)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)

The official solution for this issue is to run npm rebuild node-sass, as documented in sass/node-sass#1579. This comment suggests a yarn postinstall step to rebuild node-sass, which is the approach I took in this PR.

Checklist

- [ ] Styleguide updated, if necessary
- [ ] Swagger specification updated, if necessary
- [ ] Symlinks from new migrations present or corrected for any new migrations

Demo

N/A

Notes

Another potential option was to install the missing binary directly, as explained here. I felt that this was too hacky, and didn't fit as cleanly into the cibuild process.

Testing Instructions

• See Jenkins build output

Closes #1385

[azavea-bot]

@tnation14, thanks for your PR! By analyzing the history of the files in this pull request, we identified @notthatbreezy, @Lknechtli, @alkamin, @ddohler and @hectcastro to be potential reviewers.