Only set Base16 shell theme if `$TERM` is set.
Only set Base16 shell theme if `$TERM` is set.

There are cases where `$TERM` is not set, which can cause the theme's
commands to be printed out in a string. When `$TERM` is unset, the theme
is likely unneeded, so we can avoid setting it and triggering these
messages.

alphabetum/dotfiles,alphabetum/dotfiles,alphabetum/dotfiles,alphabetum/dotfiles