Updated autocomplete list of hub flow plugin

`git hf help` return:

```
usage: git hf <subcommand>

Available subcommands are:
   init      Initialize a new git repo with support for the branching model.
   feature   Manage your feature branches.
   release   Manage your release branches.
   hotfix    Manage your hotfix branches.
   push      Push the changes from your current branch (plus any new tags) back upstream.
   pull      Pull upstream changes down into your master, develop, and current branches.
   update    Pull upstream changes down into your master and develop branches.
   version   Shows version information.

Try 'git hf <subcommand> help' for details.
```

Added missed `help`, `push` and `pull` subcommands.