Add missing trailing slash on publicPath in docs. Fixes aspnet#516.

Author: SteveSandersonMS

src/Microsoft.AspNetCore.SpaServices/README.md

@@ -538,7 +538,7 @@ module.exports = {
 
     output: {
         path: path.join(__dirname, 'wwwroot', 'dist'),
-        publicPath: '/dist',
+        publicPath: '/dist/',
         filename: '[name].js'
     },
 };