code style: Don't use std:: inside .cpp files.
diff --git a/ndn-cpp/encoding/der/der.cpp b/ndn-cpp/encoding/der/der.cpp
index 6d269c1..fc31161 100644
--- a/ndn-cpp/encoding/der/der.cpp
+++ b/ndn-cpp/encoding/der/der.cpp
@@ -297,7 +297,7 @@
   DerNode::encodeHeader(payload_.size());
 }
 
-DerByteString::DerByteString(const std::vector<uint8_t>& blob, DerType type)
+DerByteString::DerByteString(const vector<uint8_t>& blob, DerType type)
   :DerNode(type)
 {
   payload_.insert(payload_.end(), blob.begin(), blob.end());