Fix Build Failure on Master

[pstaylor-patrick]

use gatsby 3.13.1 and webpack ^4.29.6
per issue #428 comment 962397694

[pstaylor-patrick]

🙃🚫 https://app.netlify.com/sites/gatsby-starter-ghost/deploys/61cb3a627c00f30007658ae1#L148

10:27:46 AM: failed Building production JavaScript and CSS bundles - 23.941s
10:27:46 AM: error Generating JavaScript bundles failed
10:27:46 AM: /opt/build/repo/.cache/loader.js: Missing class properties transform.
10:27:46 AM:   101 |   }
10:27:46 AM:   102 |
10:27:46 AM: > 103 |   inFlightNetworkRequests = new Map()
10:27:46 AM:       |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
10:27:46 AM:   104 |
10:27:46 AM:   105 |   memoizedGet(url) {
10:27:46 AM:   106 |     let inFlightPromise = this.inFlightNetworkRequests.get(url)
10:27:46 AM: ​
10:27:46 AM: ────────────────────────────────────────────────────────────────
10:27:46 AM:   "build.command" failed                                        
10:27:46 AM: ────────────────────────────────────────────────────────────────
10:27:46 AM: ​
10:27:46 AM:   Error message
10:27:46 AM:   Command failed with exit code 1: NODE_ENV=production gatsby build
10:27:46 AM: ​
10:27:46 AM:   Error location
10:27:46 AM:   In build.command from netlify.toml:
10:27:46 AM:   NODE_ENV=production gatsby build
10:27:46 AM: ​
10:27:46 AM:   Resolved config
10:27:46 AM:   build:
10:27:46 AM:     command: NODE_ENV=production gatsby build
10:27:46 AM:     commandOrigin: config
10:27:46 AM:     environment:
10:27:46 AM:       - AWS_LAMBDA_JS_RUNTIME
10:27:46 AM:       - REVIEW_ID
10:27:46 AM:       - SITEURL
10:27:46 AM:     publish: /opt/build/repo/public
10:27:46 AM:     publishOrigin: config

[aileen]

Thanks for the PR. Going to close this as it should be fixed with #510