Update release notes wrt #336

Author: cowtowncoder

release-notes/CREDITS-2.x

@@ -170,6 +170,8 @@ Michał Ostrowski (karbi@github)
 David Schlosnagle (schlosna@github)
  * Contributed #266: Optimize `InstantDeserializer` method `replaceZeroOffsetAsZIfNecessary()`
   (2.15.0)
+ * Contributed #336: Optimize `InstantDeserializer` `addInColonToOffsetIfMissing()`
+  (2.19.0)
 
 Daniel Scalzi (dscalzi@github)
  * Contributed #267: Normalize zone id during ZonedDateTime deserialization

release-notes/VERSION-2.x

@@ -10,7 +10,8 @@ Modules:
 
 2.19.0 (not yet released)
 
--
+#336: Optimize `InstantDeserializer` `addInColonToOffsetIfMissing()`
+ (contributed by David S)
 
 2.18.3 (not yet released)