update stb (#501)

packages/s/stb/xmake.lua

@@ -5,7 +5,7 @@ package("stb")
     set_description("single-file public domain (or MIT licensed) libraries for C/C++")
 
     add_urls("https://github.com/nothings/stb.git")
-    add_versions("0.0", "b42009b3b9d4ca35bc703f5310eedc74f584be58")
+    add_versions("0.0", "3a1174060a7dd4eb652d4e6854bc4cd98c159200")
 
     on_install(function (package)
         os.cp("*.h", package:installdir("include"))