add -- to terminate basename option (in case -bash starts with -)

```
TDWONG-M-V08D:~$ cd Workspace/GitHub/iTerm2-finna-be-octo-hipster/
TDWONG-M-V08D:iTerm2-finna-be-octo-hipster$ echo $0
-bash
TDWONG-M-V08D:iTerm2-finna-be-octo-hipster$ title
-bash: title: command not found
TDWONG-M-V08D:iTerm2-finna-be-octo-hipster$ . iterm2_helpers.sh
TDWONG-M-V08D:iTerm2-finna-be-octo-hipster$ title
ERROR: No argument provided.
Usage:
  -bash "title" to provide a new Terminal title.
TDWONG-M-V08D:iTerm2-finna-be-octo-hipster$
```
If the $0 starts with a dash (see above case), the title_help0() and title_help2() failed in providing the usage message as the basename command is confused by the leading dash.

The solution is to add '--' to end basename option list.