cvise: fix shebang for `--command=` option
Upstream `cvise` changed the way it encodes shebang from hardcoded value
to `/bin` + value:
https://github.com/marxin/cvise/commit/d99d82ce8e9d0991e629eb693f6a1187dc752938
This broke `nixpkgs` substitute hack and broke the option.
I proposed upstream to use `/usr/bin/env bash` indirection instead. This
change pulls in this proposed change.