mavlink-core: Update to 0.13.1

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

mavlink-core/Cargo.toml

 [package]
 name = "mavlink-core"
-version = "0.12.2"
+version = "0.13.1"
 authors = [
     "Todd Stellanova",
     "Michal Podhradsky",