Bump nvmrc to 20.19

[akadouri]

nvmrc has to be 20.19+ in order to run the sample app

~/basemaps/app$ nvm use
Found '~/basemaps/app/.nvmrc' with version <20.10>
Now using node v20.10.0 (npm v10.2.3)

~/basemaps/app$ npm run dev

> protomaps-basemaps-app@0.0.0 dev
> vite

You are using Node.js 20.10.0. Vite requires Node.js version 20.19+ or 22.12+. Please upgrade your Node.js version.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud