Bump go for vendor-in-container from 1.13 to 1.16

While vendoring c/storage v1.34.0 I was having issues
with io/fs not being able to be vendored via calls in the
latest BurntSushi.  Fortunately I remembered a change to
the Skopeo Makefile that @vrothberg had made recently and
viola, that fixed it.

Also per @nalind's review, I've bumped Go from 1.13 to 1.6 in the
.cirrus.yml file.

[NO NEW TESTS NEEDED]

Signed-off-by: TomSweeneyRedHat <tsweeney@redhat.com>

.cirrus.yml

@@ -120,7 +120,7 @@ vendor_task:
 
     # Runs within Cirrus's "community cluster"
     container:
-        image: docker.io/library/golang:1.13
+        image: docker.io/library/golang:1.16
         cpu: 1
         memory: 1
 

Makefile

@@ -171,7 +171,7 @@ test-unit: tests/testreport/testreport
 	$(GO_TEST) -v -tags "$(STORAGETAGS) $(SECURITYTAGS)" -cover -race ./cmd/buildah -args --root $$tmp/root --runroot $$tmp/runroot --storage-driver vfs --signature-policy $(shell pwd)/tests/policy.json --registries-conf $(shell pwd)/tests/registries.conf
 
 vendor-in-container:
-	podman run --privileged --rm --env HOME=/root -v `pwd`:/src -w /src docker.io/library/golang:1.13 make vendor
+	podman run --privileged --rm --env HOME=/root -v `pwd`:/src -w /src docker.io/library/golang:1.16 make vendor
 
 .PHONY: vendor
 vendor: