Update generated index.coffee to use fs.existsSync

Script loading should be synchronous, to preserve script load order and
allow the script to behave as expected with the `--config-check` hubot
flag. Also ensure the scripts are loaded in alphabetical order. This
matches how hubot loads scripts from the scripts/ directory.
Merge pull request #19 from kballard/patch-1

Update generated index.coffee to use fs.existsSync