Merge pull request #648 from thaJeztah/buildx_0.8

[master] update buildx to v0.8.0

Author: thaJeztah

plugins/buildx.installer

@@ -6,7 +6,7 @@ source "$(dirname "$0")/.common"
 PKG=github.com/docker/buildx
 GOPATH=$(go env GOPATH)
 REPO=https://${PKG}.git
-: "${BUILDX_COMMIT=v0.7.1}"
+: "${BUILDX_COMMIT=v0.8.0}"
 DEST=${GOPATH}/src/${PKG}
 
 build() {