Update to go1.16.6

Keeping the dockerfiles/Dockerfile.cross image at 1.13, as we don't
have more current versions of that image. However, I don't think it's
still used, so we should remove it.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

scripts/build/plugins

@@ -17,5 +17,5 @@ for p in cli-plugins/examples/* "$@" ; do
 
     echo "Building statically linked $TARGET"
     export CGO_ENABLED=0
-    go build -o "${TARGET}" --ldflags "${LDFLAGS}" "github.com/docker/cli/${p}"
+    GO111MODULE=auto go build -o "${TARGET}" --ldflags "${LDFLAGS}" "github.com/docker/cli/${p}"
 done