gatsby: [docs site] Webassembly Error When Building

Description

Documentation site was unable to build locally, encountered while trying to test #13640

Steps to reproduce

Following the directions in the docs contributions page

Expected result

Build completes without error

Actual result

cd www/
yarn install
yarn run develop

$ GATSBY_GRAPHQL_IDE=playground gatsby develop
success open and validate gatsby-configs — 0.011 s
success load plugins — 0.659 s
success onPreInit — 0.007 s
success initialize cache — 0.006 s
success copy gatsby files — 0.041 s
success onPreBootstrap — 0.015 s
success source and transform nodes — 3.982 s
success building schema — 1.366 s
success createPages — 1.387 s
success createPagesStatefully — 0.066 s
success onPreExtractQueries — 0.002 s
success update schema — 0.091 s
success extract queries from components — 0.371 s
success run static queries — 0.030 s — 4/4 136.43 queries/second
success run page queries — 0.061 s — 9/9 149.28 queries/second
success write out page data — 0.033 s
success write out redirect data — 0.001 s
success Build manifest and related icons — 0.176 s
success onPostBootstrap — 0.177 s

info bootstrap finished - 10.044 s

error UNHANDLED REJECTION

  Error: You must provide the URL of lib/mappings.wasm by calling SourceMapConsumer.initialize({ 'lib/mappings.wasm': ... }) before using SourceMapConsumer
  
  - read-wasm.js:8 readWasm
    [www]/[react-hot-loader]/[source-map]/lib/read-wasm.js:8:13
  
  - wasm.js:25 wasm
    [www]/[react-hot-loader]/[source-map]/lib/wasm.js:25:16
  
  - source-map-consumer.js:264 BasicSourceMapConsumer.then.that
    [www]/[react-hot-loader]/[source-map]/lib/source-map-consumer.js:264:14
  

Environment

  System:
    OS: macOS High Sierra 10.13.6
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
    Shell: 5.3 - /bin/zsh
  Binaries:
    Node: 11.13.0 - /usr/local/bin/node
    Yarn: 1.13.0 - /usr/local/bin/yarn
    npm: 6.9.0 - /usr/local/bin/npm
  Languages:
    Python: 3.7.1 - /Users/cameron/.pyenv/shims/python
  Browsers:
    Chrome: 74.0.3729.108
    Safari: 12.1
  npmPackages:
    gatsby: ^2.3.0 => 2.3.31 
    gatsby-image: ^2.0.5 => 2.0.40 
    gatsby-plugin-canonical-urls: ^2.0.5 => 2.0.12 
    gatsby-plugin-catch-links: ^2.0.2 => 2.0.13 
    gatsby-plugin-emotion: ^4.0.3 => 4.0.6 
    gatsby-plugin-feed: ^2.0.5 => 2.1.1 
    gatsby-plugin-google-analytics: ^2.0.5 => 2.0.18 
    gatsby-plugin-google-tagmanager: ^2.0.5 => 2.0.13 
    gatsby-plugin-guess-js: ^1.0.0 => 1.0.6 
    gatsby-plugin-layout: ^1.0.10 => 1.0.15 
    gatsby-plugin-mailchimp: ^2.2.3 => 2.2.3 
    gatsby-plugin-manifest: ^2.0.2 => 2.0.29 
    gatsby-plugin-netlify: ^2.0.0 => 2.0.15 
    gatsby-plugin-netlify-cache: ^0.1.0 => 0.1.0 
    gatsby-plugin-nprogress: ^2.0.5 => 2.0.10 
    gatsby-plugin-offline: ^2.0.22 => 2.0.25 
    gatsby-plugin-react-helmet: ^3.0.0 => 3.0.12 
    gatsby-plugin-sharp: ^2.0.5 => 2.0.35 
    gatsby-plugin-sitemap: ^2.0.1 => 2.0.12 
    gatsby-plugin-twitter: ^2.0.5 => 2.0.13 
    gatsby-plugin-typography: ^2.2.0 => 2.2.13 
    gatsby-remark-autolink-headers: ^2.0.10 => 2.0.16 
    gatsby-remark-code-titles: ^1.0.2 => 1.0.2 
    gatsby-remark-copy-linked-files: ^2.0.5 => 2.0.12 
    gatsby-remark-embed-video: ^1.7.0 => 1.7.1 
    gatsby-remark-graphviz: ^1.0.0 => 1.0.9 
    gatsby-remark-images: ^2.0.1 => 2.0.6 
    gatsby-remark-normalize-paths: ^1.0.0 => 1.0.0 
    gatsby-remark-prismjs: ^3.0.2 => 3.2.8 
    gatsby-remark-responsive-iframe: ^2.0.5 => 2.1.1 
    gatsby-remark-smartypants: ^2.0.5 => 2.0.9 
    gatsby-source-airtable: ^2.0.6 => 2.0.8 
    gatsby-source-filesystem: ^2.0.1 => 2.0.32 
    gatsby-source-npm-package-search: ^2.0.0 => 2.0.5 
    gatsby-transformer-csv: ^2.0.0 => 2.0.8 
    gatsby-transformer-documentationjs: ^3.0.0 => 3.0.1 
    gatsby-transformer-remark: ^2.2.5 => 2.3.12 
    gatsby-transformer-screenshot: ^2.0.4 => 2.0.13 
    gatsby-transformer-sharp: ^2.1.1 => 2.1.18 
    gatsby-transformer-yaml: ^2.1.1 => 2.1.12 
  npmGlobalPackages:
    gatsby-cli: 2.4.8