gitolite: update to version 3.6.12

Changelog:

2020-08-04  v3.6.12 mirroring terminoligy changes

                    install script can now modify #! lines when using a custom
                    perl executable

                    'config' user command allows for config values with spaces
                    in them

                    finally added notes in "t/README" on testing http mode and
                    mirroring, with pre-build helpers for Fedora and Manjaro

                    ...plus various bug fixes

2019-01-08  v3.6.11 fix security issue in 'rsync' (bundle helper); see commit
                    5df2b81 for more

2018-09-30  v3.6.10 fix up boo-boo caused by previous release; see mails on
                    list for details

2018-08-07  v3.6.9  prevent racy access to repos in process of migration to
                    gitolite

                    'info' learns new '-p' option to show only physical repos
                    (as opposed to wild repos)

2018-07-12  v3.6.8  fix bug when deleting *all* hooks for a repo

                    allow trailing slashes in repo names

                    make pre-receive hook driver bail on non-zero exit of a
                    pre-receive hook

                    allow templates in gitolite.conf (new feature)

                    various optimiations

2017-07-02  v3.6.7  allow repo-specific hooks to be organised into
                    subdirectories, and allow the multi-hook driver to be
                    placed in some other location of your choice

                    allow simple test code to be embedded within the
                    gitolite.conf file; see contrib/utils/testconf for how.
                    (This goes on the client side, not on the server)

                    allow syslog "facility" to be changed, from the default of
                    'local0'

                    allow @group names in config values to be expanded; it is
                    replaced with a space separated list of members

(nikita)