update fmt to 8.1.1 (#945)

packages/f/fmt/xmake.lua

@@ -4,6 +4,7 @@ package("fmt")
     set_description("fmt is an open-source formatting library for C++. It can be used as a safe and fast alternative to (s)printf and iostreams.")
 
     set_urls("https://github.com/fmtlib/fmt/releases/download/$(version)/fmt-$(version).zip")
+    add_versions("8.1.1", "23778bad8edba12d76e4075da06db591f3b0e3c6c04928ced4a7282ca3400e5d")
     add_versions("8.0.1", "a627a56eab9554fc1e5dd9a623d0768583b3a383ff70a4312ba68f94c9d415bf")
     add_versions("8.0.0", "36016a75dd6e0a9c1c7df5edb98c93a3e77dabcf122de364116efb9f23c6954a")
     add_versions("7.1.3", "5d98c504d0205f912e22449ecdea776b78ce0bb096927334f80781e720084c9f")