Replaced use of std::rand with std::mt19937

This uses a global instance of the RNG

include/internal/catch_test_case_registry_impl.cpp

@@ -28,7 +28,7 @@ namespace Catch {
                 break;
             case RunTests::InRandomOrder:
                 seedRng( config );
-                RandomNumberGenerator::shuffle( sorted );
+                std::shuffle( sorted.begin(), sorted.end(), rng() );
                 break;
             case RunTests::InDeclarationOrder:
                 // already in declaration order