Serena Williams and husband Alexis Ohanian are celebrating their anniversary with some sweet tributes.On Tuesday, Ohanian took to Instagram to share a pair of then-and-now snapshots, alongside a heartfelt message.«4 years ago you made me the happiest man in the world and our little family keeps me feeling more grateful every day,» the Reddit co-founder wrote, alongside one photo of the couple at their lavish wedding, and a second photo of the pair with their 4-year-old daughter, Alexis Olympia,