Shell: Save the history when quitting via the exit builtin

Author: https://github.com/alimpfard
Commit: abfcd7b1b8
Pull-request: https://github.com/SerenityOS/serenity/pull/2398
Reviewed-by: https://github.com/awesomekling

Shell/Shell.cpp

@@ -345,6 +345,7 @@ int Shell::builtin_exit(int, const char**)
         }
     }
     stop_all_jobs();
+    save_history();
     printf("Good-bye!\n");
     exit(0);
     return 0;