Fixes build path

I'm thinking below should be work.

```
$ kocha new github.com/mattn/foobarbaz
$ cd /path/to/my/gopath/src/github.com/mattn/foobarbaz
$ kocha b dev
$ kocha run
```

But currently, it doesn't work. It seems `kocha b dev` are looking `/path/to/my/gopath/src/foobarbaz`.