jsoncpp: Add missing <iosfwd> include in json/writer.h

The header uses std::ostream, so it must be declared.

Utilities/cmjsoncpp/include/json/writer.h

@@ -9,6 +9,7 @@
 #if !defined(JSON_IS_AMALGAMATION)
 #include "value.h"
 #endif // if !defined(JSON_IS_AMALGAMATION)
+#include <iosfwd>
 #include <vector>
 #include <string>