encoding: Deriving Block::Error from Tlv::Error

Refs: #1493

Change-Id: I1cbaa83e39538452794cebc15c8df43138ba7986
diff --git a/src/encoding/block.hpp b/src/encoding/block.hpp
index 388bac5..8079531 100644
--- a/src/encoding/block.hpp
+++ b/src/encoding/block.hpp
@@ -31,12 +31,12 @@
   typedef element_container::const_iterator  element_const_iterator;
 
   /// @brief Error that can be thrown from the block
-  class Error : public std::runtime_error
+  class Error : public Tlv::Error
   {
   public:
     explicit
     Error(const std::string& what)
-      : std::runtime_error(what)
+      : Tlv::Error(what)
     {
     }
   };