Adding "/" to MemMapFS in a cleaner way

memmap.go

diff --git a/memmap.go b/memmap.go
index 4467136..caa0cf3 100644
--- a/memmap.go
+++ b/memmap.go
@@ -48,7 +48,7 @@
 
 		// Root should always exist, right?
 		// TODO: what about windows?
-		m.getData()["/"] = &InMemoryFile{name: "/", memDir: &MemDirMap{}, dir: true}
+		m.data["/"] = &InMemoryFile{name: "/", memDir: &MemDirMap{}, dir: true}
 	}
 	return m.data
 }