Account for null values in config.basePath

Instead of reading them as a literal string 'null' it now blanks
them out. Otherwise we were getting errors like "publicnull does
not exist"! 😬

server.js

@@ -34,12 +34,15 @@ let options = {
   metaInfo: {
     title: 'Seance',
     script: [
-      { type: 'text/javascript', src: config.basePath + '/app.js' },
+      {
+        type: 'text/javascript',
+        src: (config.basePath || '') + '/app.js'
+      },
     ],
   },
   extractCSS: true,
   cssOutputPath: '/css/styles.css',
-  publicPath: 'public' + config.basePath,
+  publicPath: 'public' + (config.basePath || ''),
   compilerConfig: {
       // custom webpack config
   },