Correct version 1.83 release date (#4355)

docs/CHANGELOG.txt

@@ -99,7 +99,7 @@ Other Changes:
 
 
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- VERSION 1.83 (Released 2011-05-24)
+ VERSION 1.83 (Released 2021-05-24)
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 Decorated log: https://github.com/ocornut/imgui/releases/tag/v1.83