fix(build) fix webpack-dev-server on Windows

Allow path separator of \ in addition to / in jQuery's path name.

webpack.config.js

             // dependencies including lib-jitsi-meet.
 
             loader: 'expose-loader?$!expose-loader?jQuery',
-            test: /\/node_modules\/jquery\/.*\.js$/
+            test: /[/\\]node_modules[/\\]jquery[/\\].*\.js$/
         }, {
             // Allow CSS to be imported into JavaScript.