Fix possible file limit errors

As we currently may need higher nofile limits than usual/default on
various systems this commit should probide a fix for that an allow to
build HackMD without highering these limits and increase security.

Inspiration was found in a copy-webpack-plugin-issue[1] and found by
@thegcat[2]. Thanks for that!

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

[1]:
https://github.com/webpack-contrib/copy-webpack-plugin/issues/59#issuecomment-228563990
[2]: https://github.com/thegcat

webpackBaseConfig.js

@@ -4,6 +4,11 @@ var ExtractTextPlugin = require('extract-text-webpack-plugin')
 var HtmlWebpackPlugin = require('html-webpack-plugin')
 var CopyWebpackPlugin = require('copy-webpack-plugin')
 
+// Fix possible nofile-issues
+var fs = require('fs')
+var gracefulFs = require('graceful-fs')
+gracefulFs.gracefulify(fs)
+
 module.exports = {
   plugins: [
     new webpack.ProvidePlugin({