Lua not available to subsequent build packs

[lilith]

Scenario: Using Node+Lua together with

https://github.com/ddollar/heroku-buildpack-multi/ -> https://github.com/nathanaeljones/heroku-buildpack-lua.git https://github.com/heroku/heroku-buildpack-nodejs.git

And https://github.com/brettlangdon/NodeLua

After heroku-buildpack-lua completes, 'lua' is not available in the search path for heroku-buildpack-nodejs to successfully install NodeLua.