After npm install && npm start I get the below, running npm install --save babel-runtime allows app to run.

C:\Users\Mike\git\lossless-cut (master)
λ npm start

lossless-cut@1.0.0 start C:\Users\Mike\git\lossless-cut
electron src

App threw an error during load
Error: Cannot find module 'babel-runtime/core-js/object/assign'
at Module._resolveFilename (module.js:455:15)
at Function.Module._resolveFilename (C:\Users\Mike\git\lossless-cut\node_modules\electron-prebuilt-compile\node_modules\electron\dist\resources\electron.asar\common\reset-search-paths.js:35:12)
at Function.Module._load (module.js:403:25)
at Module.require (module.js:483:17)
at require (internal/module.js:20:19)
at Object. (C:\Users\Mike\git\lossless-cut\node_modules\electron-prebuilt-compile\node_modules\electron-compile\lib\index.js:3:15)
at Module._compile (module.js:556:32)
at Object.Module._extensions..js (module.js:565:10)
at Module.load (module.js:473:32)
at tryModuleLoad (module.js:432:12)
at Module._resolve