Update changelog

Author: Evan Fossier

CHANGES.md

@@ -3,6 +3,12 @@ twilio-python Changelog
 
 Here you can see the full list of changes between each twilio-python release.
 
+[2017-06-27] Version 6.4.2
+--------------------------
+
+- Pin PyJWT to below version `1.5.1` to fix broken build.
+- Fix json load error for python 3.3 - 3.5
+
 [2017-06-16] Version 6.4.1
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