Prefer std::variant in StaticSchema

Change-Id: Ib9c048fd7175ce551f597e8af050388263fee847
diff --git a/src/static_schema.hpp b/src/static_schema.hpp
index 3acefc0..3e01e38 100644
--- a/src/static_schema.hpp
+++ b/src/static_schema.hpp
@@ -43,7 +43,7 @@
 };
 }
 
-using NodeType = boost::variant<yang::container, yang::list, yang::leaf, yang::leaflist, yang::module>;
+using NodeType = std::variant<yang::container, yang::list, yang::leaf, yang::leaflist, yang::module>;
 
 struct NodeInfo {
     NodeType m_nodeType;