Add changelog entry for Vue 3 support

Author: foxbenjaminfox

CHANGELOG.md

@@ -2,6 +2,7 @@
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 # Changelog
 
+- [v4.0.0](#v400)
 - [v3.9.0](#v390)
 - [v3.8.1](#v381)
 - [v3.8.0](#v380)
@@ -30,6 +31,10 @@
 
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+### v4.0.0
+ * Add support for Vue 3.
+ * Drop support for Vue 2.
+
 ### v3.9.0
  * [#95](https://github.com/foxbenjaminfox/vue-async-computed/pull/95) Fix a bug where default values weren't properly used properly for lazy async computed properties.