Fixing autocomplete when using Zsh with bashcompinit wrapper

[otahontas]

Related to Issue #401 : when sourcing tmc-autocomplete and allowing 'bashcompinit' function in zshrc file, tmc autocompletion errors with "tmc _tmc_opts:10: unrecognized modifier `C'".

Apparently "${COMP_WORDS[@]:0:COMP_CWORD}" and
"${COMP_WORDS[@]:0:$COMP_CWORD}" aren't the same in zsh (according to: openshift/rhc#729).

Fixing line 17 in tmc-cli/scripts/autocompletion.sh does seem to fix the issue on zsh and preserves expected behaviour on bash.