!567 prioritize json downloading from gitee

From: @nicholas_yhr
Reviewed-by: @liujunzhu,@youui
Signed-off-by: @youui

cmake/external_libs/json.cmake

@@ -5,15 +5,15 @@ endif()
 include(ExternalProject)
 
 set(JSON_SRC_DIR ${CMAKE_BINARY_DIR}/opensrc/json/include)
-#if (ENABLE_GITEE)
-#    set(REQ_URL "https://gitee.com/mirrors/JSON-for-Modern-CPP/repository/archive/v3.6.1.zip")
-#    set(MD5 "5bda78ce308e6cfcf614dcf1d5ff27a7")
-#    set(JSON_INCLUDE_DIR "${JSON_SRC_DIR}/include")
-#else()
-set(REQ_URL "https://github.com/nlohmann/json/releases/download/v3.6.1/include.zip")
-set(MD5 "0dc903888211db3a0f170304cd9f3a89")
-set(JSON_INCLUDE_DIR ${JSON_SRC_DIR})
-#endif ()
+if (ENABLE_GITEE)
+    set(REQ_URL "https://gitee.com/mirrors/JSON-for-Modern-CPP/repository/archive/v3.6.1.zip")
+    set(MD5 "5bda78ce308e6cfcf614dcf1d5ff27a7")
+    set(JSON_INCLUDE_DIR "${JSON_SRC_DIR}/include")
+else()
+    set(REQ_URL "https://github.com/nlohmann/json/releases/download/v3.6.1/include.zip")
+    set(MD5 "0dc903888211db3a0f170304cd9f3a89")
+    set(JSON_INCLUDE_DIR ${JSON_SRC_DIR})
+endif ()
 ExternalProject_Add(json_build
                     URL ${REQ_URL}
                     #URL /home/txd/workspace/cloud_code/pkg/include.zip