Support tmux session titles with non alphanumeric characters

[Hervé MARTIN]

Attach session with a non alphanumeric name is not working.
For example : if I select a tmux session named 'private_dotfiles', I get this error :
.tmux/plugins/tmux-fzf/scripts/session.sh' returned 123
I'll submit a PR soon, it's a regexp pb.

[Sainnhe Park]

Thanks for your fix! This PR has been merged.