chore(linter): Make the mandatory linters happy

There are some new linting rules in the updated go-dev from upstream
deis/docker-go-dev.

pkg/gitreceive/build.go

@@ -354,7 +354,7 @@ func prettyPrintJSON(data interface{}) (string, error) {
 	if err := json.Indent(formatted, output.Bytes(), "", "  "); err != nil {
 		return "", err
 	}
-	return string(formatted.Bytes()), nil
+	return formatted.String(), nil
 }
 
 func getProcFile(getter storage.ObjectGetter, dirName, procfileKey string, bType buildType) (deisAPI.ProcessType, error) {

pkg/gitreceive/k8s_util.go

@@ -326,10 +326,13 @@ func createAppEnvConfigSecret(secretsClient client.SecretsInterface, secretName
 	}
 	if _, err := secretsClient.Create(newSecret); err != nil {
 		if apierrors.IsAlreadyExists(err) {
-			if _, err = secretsClient.Update(newSecret); err != nil {
-				return err
-			}
-			return nil
+			_, err = secretsClient.Update(newSecret)
+			// I simplified according to linter, err is either "err" or nil
+			// So no need for an if-statement here, as before with the redundant if
+			// statement, it was either returning err or nil just the same...
+			return err
+			// KPB: I actually don't agree with this simplification, but I don't know
+			// how to make the linter ignore it yet...
 		}
 		return err
 	}

pkg/sshd/server_test.go

@@ -22,7 +22,7 @@ func TestGitPktLine(t *testing.T) {
 	err := gitPktLine(b, str)
 	assert.NoErr(t, err)
 
-	outStr := string(b.Bytes())
+	outStr := b.String()
 	assert.True(t, len(outStr) > 4, "output string <= 4 chars")
 	assert.Equal(t, outStr[:4], fmt.Sprintf("%04x", len(str)+4), "hex prefix")
 	assert.Equal(t, outStr[4:], str, "remainder of string")
@@ -279,7 +279,7 @@ func gitPktLineStr(str string) (string, error) {
 	if err := gitPktLine(&buf, str); err != nil {
 		return "", err
 	}
-	return string(buf.Bytes()), nil
+	return buf.String(), nil
 }
 
 // connMetadata mocks ssh.ConnMetadata for authentication.

pkg/storage/object_test.go

@@ -15,7 +15,7 @@ const (
 )
 
 func TestObjectExistsSuccess(t *testing.T) {
-	objInfo := storagedriver.FileInfoInternal{storagedriver.FileInfoFields{Path: objPath, Size: 1234}}
+	objInfo := storagedriver.FileInfoInternal{FileInfoFields: storagedriver.FileInfoFields{Path: objPath, Size: 1234}}
 	statter := &FakeObjectStatter{
 		Fn: func(context.Context, string) (storagedriver.FileInfo, error) {
 			return objInfo, nil