fix bug in nightly-release script
#!/bin/sh -ex
git fetch k '+refs/heads/*:refs/remotes/k/*'
-test `git rev-parse HEAD:$(dirname $0)/../../../` = `git rev-parse refs/remotes/k/master^{tree}`
+test `git rev-parse HEAD:k` = `git rev-parse refs/remotes/k/master^{tree}`
COMMIT=$(git rev-parse --short k/master)
DESCRIPTION='This is the nightly release of the K framework. To install, download and extract the "Prebuilt K binary", and follow the instructions in INSTALL.md within the target directory. On Windows, start by installing [Windows Subsystem for Linux](https://docs.microsoft.com/en-us/windows/wsl/install-win10) with Ubuntu, after which you can download and extract the archive by running:
```
