Prune any past devDependencies, if present in cache

If the --production flag is specified, this command will remove the packages specified in your devDependencies.

https://www.npmjs.org/doc/cli/npm-prune.html

bin/compile

@@ -66,7 +66,7 @@ elif test -d $cache_dir/node/node_modules; then
   cp -r $cache_dir/node/node_modules $build_dir/
 
   status "Pruning cached dependencies not specified in package.json"
-  npm prune 2>&1 | indent
+  npm prune --production 2>&1 | indent
 
   if test -f $cache_dir/node/.heroku/node-version && [ $(cat $cache_dir/node/.heroku/node-version) != "$node_version" ]; then
     status "Node version changed since last build; rebuilding dependencies"