docs: Fix wrong version number in the release notes

Change-Id: I7d00c2fd95c7363bcc95497d34f3e4ac140cbc11
Refs: #4275
diff --git a/docs/release-notes/release-notes-0.6.0.rst b/docs/release-notes/release-notes-0.6.0.rst
index 8510ad2..f774775 100644
--- a/docs/release-notes/release-notes-0.6.0.rst
+++ b/docs/release-notes/release-notes-0.6.0.rst
@@ -1,4 +1,4 @@
-ndn-cxx version 0.5.1
+ndn-cxx version 0.6.0
 ---------------------
 
 Release date: October 16, 2017