Serverless 0.5.x compatibility

[martinmicunda]

This plugin doesn't seem to work with latest serverless v0.5.0.

/node_modules/bluebird/js/release/async.js:49
        fn = function () { throw arg; };
                           ^

TypeError: Path must be a string. Received undefined
  at assertPath (path.js:8:11)
  at Object.posix.join (path.js:479:5)

[hideyuki]

I fixed this issue and made the pull request #11

[jjmartin]

i think your pull request is in the latest 1.3 version but its still not working for me