Missing dependency to build the image docker

[imTHAI]

Hello,

As with issue #91, we get an error message saying that a package is missing.

 > [6/7] RUN npm run build:
0.525
0.525 > [email protected] build /usr/src/node-app
0.525 > react-scripts build && rm -rf release/public && mkdir release/public && mv -v build/* ./release/public && cp release/public/index.html release/public/login.html
0.525
0.866 internal/modules/cjs/loader.js:484
0.866       throw e;
0.866       ^
0.866
0.866 Error: Cannot find module '/usr/src/node-app/node_modules/@jridgewell/gen-mapping/dist/gen-mapping.umd.js'

I fixed the problem by adding the following to packages.json ‘@jridgewell/gen-mapping: ‘0.3.5

(Proposed pull request: #103)