Update to fix lint errors

Context should use type values instead of strings.
Updated direct calls to WithValue, but still other uses of string keys.
Update Acl to ACL in s3 driver.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

registry/auth/silly/access_test.go

@@ -16,7 +16,7 @@ func TestSillyAccessController(t *testing.T) {
 	}
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		ctx := context.WithValue(nil, "http.request", r)
+		ctx := context.WithRequest(context.Background(), r)
 		authCtx, err := ac.Authorized(ctx)
 		if err != nil {
 			switch err := err.(type) {