fix typo in a comment (vuejs-templates#1183)

Author: dennybiasiolli

template/build/webpack.prod.conf.js

@@ -78,7 +78,7 @@ const webpackConfig = merge(baseWebpackConfig, {
       // necessary to consistently work with multiple chunks via CommonsChunkPlugin
       chunksSortMode: 'dependency'
     }),
-    // keep module.id stable when vender modules does not change
+    // keep module.id stable when vendor modules does not change
     new webpack.HashedModuleIdsPlugin(),
     // enable scope hoisting
     new webpack.optimize.ModuleConcatenationPlugin(),