OptimizedLoadingServer throws error due to babel-core

[levjj]

This error does not seem critical but it shows up when initializing the optimized cache. It seems that it relies on a file babel-core/browser.js which is missing from the latest version of babel-core.

Reproduce: Install Lively in a clean localhost environment and run npm run start.

[ERROR] console - optimized-loading-cache initialization errored Error: ENOENT: no such file or directory, stat 'node_modules/lively.modules/node_modules/babel-core/browser.js'
    at Error (native)
    at Object.fs.statSync (fs.js:892:18)
    at /home/cs/Projects/lively/LivelyKernel/core/servers/OptimizedLoadingServer.js:78:27
    at prepareFileForConcat (/home/cs/Projects/lively/LivelyKernel/core/servers/OptimizedLoadingServer.js:68:10)
    at /home/cs/Projects/lively/LivelyKernel/core/servers/OptimizedLoadingServer.js:111:37
    at Array.map (native)
    at concatAndWrite (/home/cs/Projects/lively/LivelyKernel/core/servers/OptimizedLoadingServer.js:111:28)
    at /home/cs/Projects/lively/LivelyKernel/core/servers/OptimizedLoadingServer.js:53:11
    at resolveNext (/home/cs/Projects/lively/lively.lang/lib/promise.js:134:25)
    at /home/cs/Projects/lively/lively.lang/lib/promise.js:135:34