build: align minimum build dependencies with ndn-cxx

 * gcc 7.4
 * clang 6.0
 * Xcode 10.0 (11.3 or later recommended)

Change-Id: I365e7b1e2c9b081e512f511bf5beee2487cfc361
diff --git a/docs/conf.py b/docs/conf.py
index 495d441..5b7a5ae 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -18,7 +18,7 @@
 # -- Project information -----------------------------------------------------
 
 project = u'PSync: Full/Partial Synchronization Protocol for NDN'
-copyright = u'Copyright © 2018-2021 Named Data Networking Project.'
+copyright = u'Copyright © 2018-2022 Named Data Networking Project.'
 author = u'Named Data Networking Project'
 
 # The short X.Y version.