They deleted a commit in master
https://github.com/hashicorp/yamux/issues/65

Add "firmware" as an option for the hardware section, allowing values of
"efi" or "bios" (default "bios") so that the firmware is defined at the
machine create stage.

Fix #107 RPC client in the plugin uses incompatible version of a message codec, so Packer core cannot read them

This reverts commit 1eaebb15

Windows sends XML documents without `<?xml ?>` header.
goxpath library supported it in https://github.com/ChrisTrenkamp/goxpath/commit/e2e5bcefc4e07f4a0c587a1200c22665dd39bd0e

(cherry picked from commit 8866411)