release: 0.2.0

Move the version down from 0.3.0; I bumped it to 0.3 in
#93 but forgot that we
never did a 0.2 release, so no need to skip that version number.

Author: nicholasbishop

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "ovmf-prebuilt"
-version = "0.3.0"
+version = "0.2.0"
 edition.workspace = true
 categories = ["development-tools"]
 keywords = ["edk2", "firmware", "ovmf", "prebuilt"]