Sensible permissions on creating a file

Open a file, create it if it doesn't exist, and for gods sake don't leave it 0666.

physical/file.go

@@ -84,7 +84,7 @@ func (b *FileBackend) Put(entry *Entry) error {
 	}
 
 	// JSON encode the entry and write it
-	f, err := os.Create(filepath.Join(path, key))
+	f, err := os.OpenFile(filepath.Join(path, key), os.O_CREATE|os.O_TRUNC, 0600)
 	if err != nil {
 		return err
 	}