Set NODE_ENV to support build with npm & Yarn.

Author: mars

bin/compile

@@ -32,8 +32,9 @@ dir=$(mktemp -t buildpackXXXXX)
 rm -rf $dir
 
 # Set env vars for the inner buildpacks in `.buildpacks`
-# * Install `npm build` tooling.
-export NPM_CONFIG_PRODUCTION=false
+# * install build tooling (devDependencies) with npm & Yarn
+# * used only during compile, as the runtime is a static web server
+export NODE_ENV=development
 
 echo "=====> Downloading Buildpack: $url"