Update CHANGELOG.md

Add Thank You note for @tituszban

CHANGELOG.md

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+## v0.21.0 [08/25/2020]
+
+### Release Notes
+This version introduces methods to query and post strongly typed points using attributes. Thanks to @tituszban for adding the attribute support. Refer to [Readme.md](https://github.com/AdysTech/InfluxDB.Client.Net/blob/master/README.md) for examples. 
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+
 ## v0.20.0 [08/11/2020]
 
 ### Release Notes
@@ -268,4 +274,4 @@ Added the functionality to query for existing data from InfluxDB. Also unknown l
 
 ### Bugfixes
 
-- [#3](https://github.com/AdysTech/InfluxDB.Client.Net/pull/3): Double to str conversion fix, Thanks to @spamik
+- [#3](https://github.com/AdysTech/InfluxDB.Client.Net/pull/3): Double to str conversion fix, Thanks to @spamik