valijson downgrade to v4

The valijson feature branch supporting json schema v6 and v7
<https://github.com/tristanpenman/valijson/tree/v6-and-v7-support>
causes a seg fault on Linux.

3rdparty/valijson/README.md

@@ -1,7 +1,5 @@
-This README has been copied from: <https://github.com/tristanpenman/valijson>
-
-The sources used are from branch <https://github.com/tristanpenman/valijson/tree/v6-and-v7-support>.  
-Copied December 26, 2019.
+This README and sources have been copied from the master branch of <https://github.com/tristanpenman/valijson>.   
+Copied March 13, 2020.
 
 - only the include directory has been copied
 - examples and testsuite were omitted

3rdparty/valijson/include/valijson/adapters/jsoncpp_adapter.hpp

@@ -706,7 +706,7 @@ inline JsonCppObjectMemberIterator JsonCppObject::find(
 {
     if (value.isMember(propertyName)) {
         Json::ValueConstIterator itr;
-        for (itr = value.begin(); itr != value.end(); ++itr) {
+        for ( itr = value.begin(); itr != value.end(); ++itr) {
             if (itr.key() == propertyName) {
                 return itr;
             }

3rdparty/valijson/include/valijson/adapters/property_tree_adapter.hpp

@@ -283,8 +283,9 @@ class PropertyTreeValue
                 array.emplace(tree);         // Treat as empty array
             } else {
                 bool isArray = true;
-                for (const auto node : tree) {
-                    if (!node.first.empty()) {
+                boost::property_tree::ptree::const_iterator itr;
+                for (itr = tree.begin(); itr != tree.end(); itr++) {
+                    if (!itr->first.empty()) {
                         isArray = false;
                         break;
                     }