Fixed building static in case of absolute output

path.join is unsafe when using absolute paths after first argument.
For resolving from cwd path.resolve function is safe and makes correct results in both cases, using absolute or relative paths.

lib/core/src/server/preview/iframe-webpack.config.js

@@ -37,7 +37,7 @@ export default ({
     devtool: '#cheap-module-source-map',
     entry: entries,
     output: {
-      path: path.join(process.cwd(), outputDir),
+      path: path.resolve(process.cwd(), outputDir),
       filename: '[name].[hash].bundle.js',
       publicPath: '',
     },