stage1: gitignore stage1/cache

just started fooling around with the repo and noticed this maybe missing from the gitignore
This should end with a slash since it's a directory, not a file. From http://git-scm.com/docs/gitignore:
> If the pattern ends with a slash...it would only find a match with a directory .`foo/` will match a directory `foo` and paths underneath it, but will not match a regular file or a symbolic link `foo`.