Fixed parser name. Fixed Gemfile and Rakefile.

[andreamazz]

Hi @0xfe
I made some minor changes to your library. First of all I fixed an issue with the naming of the parser exported by vextab.coffee, that was causing the vextab_parser is undefined as mentioned in issue #49 and also was failing all the tests.
I also switched the sh command in the Rakefile, migrating to the backquote command. This was causing an issue when running the rake tasks in a ZSH shell, using rbenv (the wrong ruby was called).
I removed therubyracer from the Gemfile, and added libv8 instead. therubyracer has some issues right now with OsX Yosemite.

Thanks for your great work.
Cheers

[0xfe]

Thanks for the PR. I'm not sure why vextab_parser is undefined for you -- it works for me, and looking at the generated build/output/vextab_parser.js, I can see where it is defined. Maybe something changed in jison?

Also, backquotes typically chew up standard output, so I don't think it's a good replacement for sh. Can you see the output of the commands that are run?

[andreamazz]

Looks like there was an update 12 days ago (version 0.4.15), that might be it. A fresh clone of this repo with a fresh install raises the problem mentioned in Issue #49.

As for the backquote operator, I can see the output fine (running ruby 2.1.2). A call to system might be valid alternatives though, as long as the current environment is kept.

[andrewtevinkim]

Can confirm a fresh clone raises the same problem, and andreamazz's fork fixes it.

[eerwitt]

@andreamazz I made a new pull request before seeing yours, I have the same problem with a fresh clone and switching to your branch works perfect. Thank you.

[0xfe]

Parser name is fixed. I'm overhauling the build system (moving to Grunt, like VexFlow), which should resolve most of these issues. Thanks for the PR!