Instructions for contributing fail at `npm run start`

[woahdae]

Everything succeeds to this point, and additionally npm run test successfully runs the jest tests.

Output:

[git/master-]:keen-dataviz.js% npm run start

> keen-dataviz@3.13.8 start /Users/woody/Src/keen-dataviz.js
> concurrently --kill-others "NODE_ENV=development webpack-dev-server" "npm run postcss-watch"

[1] 
[1] > keen-dataviz@3.13.8 postcss-watch /Users/woody/Src/keen-dataviz.js
[1] > node_modules/postcss-cli/bin/postcss lib/style/keen-dataviz-c3.css -o test/demo/keen-dataviz.css --watch --config postcss.config.js
[1] 
[0] internal/modules/cjs/loader.js:626
[0]     throw err;
[0]     ^
[0] 
[0] Error: Cannot find module '../demo-config'
[0] Require stack:
[0] - /Users/woody/Src/keen-dataviz.js/webpack.config.js
[0] - /Users/woody/Src/keen-dataviz.js/node_modules/webpack-cli/bin/utils/convert-argv.js
[0] - /Users/woody/Src/keen-dataviz.js/node_modules/webpack-dev-server/bin/webpack-dev-server.js
[0]     at Function.Module._resolveFilename (internal/modules/cjs/loader.js:623:15)
[0]     at Function.Module._load (internal/modules/cjs/loader.js:527:27)
[0]     at Module.require (internal/modules/cjs/loader.js:681:19)
[0]     at require (internal/modules/cjs/helpers.js:16:16)
[0]     at Object.<anonymous> (/Users/woody/Src/keen-dataviz.js/webpack.config.js:14:22)
[0]     at Module._compile (internal/modules/cjs/loader.js:774:30)
[0]     at Object.Module._extensions..js (internal/modules/cjs/loader.js:785:10)
[0]     at Module.load (internal/modules/cjs/loader.js:641:32)
[0]     at Function.Module._load (internal/modules/cjs/loader.js:556:12)
[0]     at Module.require (internal/modules/cjs/loader.js:681:19) {
[0]   code: 'MODULE_NOT_FOUND',
[0]   requireStack: [
[0]     '/Users/woody/Src/keen-dataviz.js/webpack.config.js',
[0]     '/Users/woody/Src/keen-dataviz.js/node_modules/webpack-cli/bin/utils/convert-argv.js',
[0]     '/Users/woody/Src/keen-dataviz.js/node_modules/webpack-dev-server/bin/webpack-dev-server.js'
[0]   ]
[0] }
[0] NODE_ENV=development webpack-dev-server exited with code 1
--> Sending SIGTERM to other processes..
[1] npm run postcss-watch exited with code null
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! keen-dataviz@3.13.8 start: `concurrently --kill-others "NODE_ENV=development webpack-dev-server" "npm run postcss-watch"`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the keen-dataviz@3.13.8 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/woody/.npm/_logs/2020-05-12T23_53_30_339Z-debug.log