[Fix #163] Selectively set terminal title in preexec

Apple Terminal will now reset the terminal title after a command has finished
executing.

modules/terminal/init.zsh

@@ -102,8 +102,10 @@ add-zsh-hook precmd set-title-precmd
 # Sets the tab and window titles before command execution.
 function set-title-preexec {
   if zstyle -t ':omz:module:terminal' auto-title; then
+    if [[ "$TERM_PROGRAM" != 'Apple_Terminal' ]]; then
       set-title-by-command "$2"
     fi
+  fi
 }
 add-zsh-hook preexec set-title-preexec