Fix changelog formatting

Author: phil-opp

Changelog.md

@@ -4,7 +4,7 @@
 
 # 0.9.16 – 2021-03-07
 
-Replace all remaining `lea`s with `mov` + `offset` ([#140](https://github.com/rust-osdev/bootloader/pull/140))
+- Replace all remaining `lea`s with `mov` + `offset` ([#140](https://github.com/rust-osdev/bootloader/pull/140))
 
 # 0.9.15 – 2021-03-07