Updated webpack config to cleanup warnings

no refs

`yarn build` used to throw up a lot of warnings because the webpack config was not correctly updated to use performance config for portal's usecase, this change -

- Sets the `mode` to explicit `production` instead of implicit which throws a warning
- Updated performance max* sizes to account for a single portal chunk bundled up as an external script

ghost/portal/webpack.config.js

@@ -2,6 +2,7 @@ const path = require('path');
 const glob = require('glob');
 
 module.exports = {
+    mode: 'production',
     entry: {
         'bundle.js': glob.sync('build/static/?(js|css)/main.*.?(js|css)').map(f => path.resolve(__dirname, f))
     },
@@ -17,5 +18,10 @@ module.exports = {
             }
         ]
     },
-    plugins: []
+    plugins: [],
+    performance: {
+        hints: false,
+        maxEntrypointSize: 560,
+        maxAssetSize: 5600
+    }
 };