Begin development for v0.13

Signed-off-by: Ondrej Fabry <ondrej@fabry.dev>

Author: ondrej-fabry

internal/version/version.go

@@ -28,7 +28,7 @@ import (
 // even with bare go build/install.
 var (
 	name       = "govpp"
-	version = "v0.12.0"
+	version    = "v0.13.0-dev"
 	commit     = "unknown"
 	branch     = "HEAD"
 	buildStamp = ""