grails: 3.3.5 -> 3.3.6

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/grails/versions.

These checks were done:

- built on NixOS
- Warning: no invocation of /nix/store/sp0w4frknlgjhmw18j8rsj5sgaf95zhm-grails-3.3.6/bin/grails had a zero exit code or showed the expected version
- 0 of 1 passed binary check by having a zero exit code.
- 0 of 1 passed binary check by having the new version present in output.
- found 3.3.6 with grep in /nix/store/sp0w4frknlgjhmw18j8rsj5sgaf95zhm-grails-3.3.6
- directory tree listing: https://gist.github.com/8278e7c1c9d28a8983fdaf23975bb930
- du listing: https://gist.github.com/10a146e1e865583f68e892f13c310026