Dockerfile.buildx: update buildx to v0.5.1

full diff: https://github.com/docker/buildx/compare/v0.3.1...v0.5.1

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 30b20a6bdd6ea3439da9b44bd15e34f679530fbe)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile.buildx

@@ -1,5 +1,5 @@
 ARG GO_VERSION=1.13.15
-ARG BUILDX_COMMIT=v0.3.1
+ARG BUILDX_COMMIT=v0.5.1
 ARG BUILDX_REPO=https://github.com/docker/buildx.git
 
 FROM golang:${GO_VERSION}-buster AS build