Fix version and date in CHANGELOG.md

The changes for the previous version were mistakenly attributed to 0.5.0, while actually they belong to 0.6.0. This release date is fixed as well.

Author: MaxDesiatov

CHANGELOG.md

@@ -24,7 +24,7 @@
 - Add `JSDate` implementation with tests ([#45](https://github.com/swiftwasm/JavaScriptKit/pull/45)) via [@MaxDesiatov](https://github.com/MaxDesiatov)
 - Add `JSError` with tests, add JSObject.description ([#47](https://github.com/swiftwasm/JavaScriptKit/pull/47)) via [@MaxDesiatov](https://github.com/MaxDesiatov)
 
-# 0.5.0 (18 July 2020)
+# 0.6.0 (11 September 2020)
 
 This release adds `JSTypedArray` generic type, renames `JSObjectRef` to `JSObject`, and makes `JSClosure` memory management more explicit.