Only do the symlink if envdir is passed in and you're setting this stuff
up

As it is now we can't use this buildpack in non dyno environments w/o
/app
idempotent symlink

The official interface doc for buildpacks[1] doesn't say
that buildpacks always run in a fresh container or
anything of the like, so we ought to assume that things
we did in previous invocations might stick around.

[1]: https://devcenter.heroku.com/articles/buildpack-api
export GO_GIT_DESCRIBE_SYMBOL from env_dir

Removing the special case treatment of this entry fixes
building in environments without env_dir support.
update to newer godep
trying to use make to build client side