libdot: release 1.21

Change-Id: I2c5b230989d16e0dc7c940a768109b0a46c1bb7c

Author: vapier

libdot/doc/ChangeLog.md

@@ -1,3 +1,9 @@
+# 1.21, 2018-01-05, Minor fixes.
+
+* Fix storage write callbacks with shallow prefs.
+* Add helper script for filtering NaCl plugins for distribution.
+* Set charset=utf-8 in html files.
+
 # 1.20, 2017-12-13, Features & fixes.
 
 * refactor ranges.py for better modularity