A former White House press secretary — who made waves at the Democratic National Convention this week over her stinging rebuke of Donald Trump — mocked her former boss on Friday night after he boasted about being up in one poll. Trump took to his social media site Truth Social to brag in all capital letters that he was “FIVE POINTS UP OVER KAMALA IN THE JUST RELEASED RASMUSSEN POLL. MAKE AMERICA GREAT AGAIN!” The post caught the attention of Stephanie Grisham, who on Tuesday shared at the DNC on Tuesday night she wasn’t just a Trump supporter, she was a “true believer” and one of his closest a…