when command_execution_time is a single integer, add 's' suffix to it

Inspired by Powerlevel9k/powerlevel9k#1215.

Author: romkatv

internal/p10k.zsh

@@ -677,7 +677,8 @@ prompt_command_execution_time() {
 
   if (( _P9K_COMMAND_DURATION < 60 )); then
     if [[ $POWERLEVEL9K_COMMAND_EXECUTION_TIME_PRECISION == 0 ]]; then
-      local -i text=_P9K_COMMAND_DURATION
+      local -i sec=_P9K_COMMAND_DURATION
+      local text=${sec}s
     else
       local -F $POWERLEVEL9K_COMMAND_EXECUTION_TIME_PRECISION text=_P9K_COMMAND_DURATION
     fi