main: Deconfuse $EDITOR

Work around <https://github.com/chrisbra/vim-zsh/issues/33>.

highlighters/main/main-highlighter.zsh

@@ -659,7 +659,7 @@ _zsh_highlight_main_highlighter_highlight_list()
 
     if (( $#in_alias == 0 && in_param == 0 )); then
       # Compute the new $start_pos and $end_pos, skipping over whitespace in $buf.
-      [[ "$proc_buf" = (#b)(#s)(([ $'\t']|[\\]$'\n')#)(?|)* ]]
+      [[ "$proc_buf" = (#b)(#s)(''([ $'\t']|[\\]$'\n')#)(?|)* ]]
       # The first, outer parenthesis
       integer offset="${#match[1]}"
       (( start_pos = end_pos + offset ))