add github url for yaml-cpp (#2018)

packages/y/yaml-cpp/xmake.lua

@@ -4,7 +4,8 @@ package("yaml-cpp")
     set_description("A YAML parser and emitter in C++")
     set_license("MIT")
 
-    add_urls("https://github.com/jbeder/yaml-cpp/archive/yaml-cpp-$(version).tar.gz")
+    add_urls("https://github.com/jbeder/yaml-cpp/archive/yaml-cpp-$(version).tar.gz",
+             "https://github.com/jbeder/yaml-cpp.git")
     add_versions("0.6.3", "77ea1b90b3718aa0c324207cb29418f5bced2354c2e483a9523d98c3460af1ed")
     add_versions("0.7.0", "43e6a9fcb146ad871515f0d0873947e5d497a1c9c60c58cb102a97b47208b7c3")