Export App Fails

[ruucm-working]

It shows below error repeatedly

./~/core-js/shim.js
Module build failed: Error: ENOENT: no such file or directory, open '/Users/mac/Desktop/structor/node_modules/core-js/shim.js'
 @ ./~/babel-polyfill/lib/index.js 3:0-23
 @ ./.structor/src/default.js
 @ multi react-hot-loader/patch eventsource-polyfill webpack-hot-middleware/client?path=/structor-dev/a&timeout=2000&overlay=false&noInfo=true ./.structor/src/default.js
./~/core-js/fn/regexp/escape.js
Module build failed: Error: ENOENT: no such file or directory, open '/Users/mac/Desktop/structor/node_modules/core-js/fn/regexp/escape.js'
 @ ./~/babel-polyfill/lib/index.js 7:0-35
 @ ./.structor/src/default.js
 @ multi react-hot-loader/patch eventsource-polyfill webpack-hot-middleware/client?path=/structor-dev/a&timeout=2000&overlay=false&noInfo=true ./.structor/src/default.js