unique_ptr/new to make_unique

The latter is easier to read and is the "correct" thing to do.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/tag/Builder.cxx

@@ -158,7 +158,7 @@ TagBuilder::Commit() noexcept
 std::unique_ptr<Tag>
 TagBuilder::CommitNew() noexcept
 {
-	std::unique_ptr<Tag> tag(new Tag());
+	auto tag = std::make_unique<Tag>();
 	Commit(*tag);
 	return tag;
 }