Clean config register before reading in from file in order to avoid stale values

viper.go

diff --git a/viper.go b/viper.go
index b23d837..e099839 100644
--- a/viper.go
+++ b/viper.go
@@ -677,6 +677,8 @@
 		return err
 	}
 
+	v.config = make(map[string]interface{})
+
 	v.marshalReader(bytes.NewReader(file), v.config)
 	return nil
 }