Enable goimports check

Validates that goimports has been run on all files

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

registry/storage/driver/middleware/cloudfront/s3filter_test.go

@@ -5,13 +5,14 @@ import (
 	"crypto/rand"
 	"encoding/json"
 	"fmt"
-	dcontext "github.com/docker/distribution/context"
 	"net"
 	"net/http"
 	"net/http/httptest"
 	"testing"
 	"time"
 
+	dcontext "github.com/docker/distribution/context"
+
 	"reflect" // used as a replacement for testify
 )