Upgrade catch2 to 2.13.6 (#449)

* Upgrade catch2 to 2.13.6

* Update xmake.lua

packages/c/catch2/xmake.lua

@@ -4,6 +4,7 @@ package("catch2")
     set_description("Catch2 is a multi-paradigm test framework for C++. which also supports Objective-C (and maybe C). ")
 
     add_urls("https://github.com/catchorg/Catch2/archive/v$(version).zip")
+    add_versions("2.13.6", "39d50f5d1819cdf2908066664d57c2cde4a4000c364ad3376ea099735c896ff4")
     add_versions("2.13.5", "728679b056dc1248cc79b3a1999ff7453f76422c68417563fc47a0ac2aaeeaef")
     add_versions("2.9.2", "dc486300de22b0d36ddba1705abb07b9e5780639d824ba172ddf7062b2a1bf8f")