unable to deploy missing Webpack

[jsj14]

Deployment fails with missing webpack library
A clear and concise description of what the bug is.

2:43:31 PM: error There was a problem loading the local build command. Gatsby may not be installed. Perhaps you need to run "npm install"? Cannot find module 'webpack'
2:43:31 PM: 
2:43:31 PM:   Error: Cannot find module 'webpack'
2:43:31 PM:   
2:43:31 PM:   - loader.js:636 Function.Module._resolveFilename
2:43:31 PM:     internal/modules/cjs/loader.js:636:15
2:43:31 PM:   

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Netlify to deploy latest push'
2. Click on 'Deploy Site' if not already being deployed (continuous integration)
3. Click on Production deploys that failed to expand it with logs for that attempt.
4. Scroll down the 'logs' until you see this error in red.
5. See error

Expected behavior
all downloads and installations were done as per the documentation and this deployment should have been easier and straightforward.
Screenshots

Desktop (please complete the following information):

• OS: [e.g. iOS] Mac
• Browser [e.g. chrome, safari] Google Chrome
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.