Update changelog for yanked 0.11.3

Author: phil-opp

Changelog.md

@@ -1,9 +1,11 @@
 # Unreleased
 
-# 0.11.3 – 2020-09-01
-
 - Add a function for the `nop` instruction ([#174](https://github.com/rust-osdev/x86_64/pull/174))
 
+# ~~0.11.3 – 2020-09-01~~
+
+- (accidental release, yanked)
+
 # 0.11.2 – 2020-08-13
 
 - Add rdfsbase, rdgsbase, wrfsbase, wrgsbase ([#172](https://github.com/rust-osdev/x86_64/pull/172))