optimize.js | splitChunks rules: need handle node_modules in windows

[derekhu]

easywebpack/lib/core/optimize.js

Line 40 in 9874cf7

files.unshift(`node_modules/_?(${modules.join('|')})(@|/)`);

files.unshift(node_modules/_?(${modules.join('|')})(@|/));

should be: node_modules[\\/] etc.

otherwise: splitChunks won't work in develpment phase for windows.