Load Bash compl even if `__gitcomp` already exists

In `lib/git-hub.d/init`, load the Bash completion facilities for `git
hub` regardless of whether the `__gitcomp` Bash function, defined by the
standard Git completion script, was already available without
`lib/git-hub.d/init` needing to source the standard Git completion
script.

Previously, the Bash completion facilities for `git hub` would only be
loaded if `__gitcomp` was not available prior to `lib/git-hub.d/init`’s
execution, which did not seem to me to be the desired behavior.
Merge pull request #143 from 8573/8573/fix/shell-env-init-script/load-bash-compl-even-if-gitcomp-already-loaded/1

Load Bash compl even if `__gitcomp` already exists