fix branch switch notice

Author: frantuma

README.md

@@ -1,6 +1,6 @@
 # Swagger Parser
 
-**NOTE:** If you're looking for `swagger-parser` 1.X and OpenApi 2.0, please refer to [v1 branch](https://github.com/swagger-api/swagger-core/tree/v1)
+**NOTE:** If you're looking for `swagger-parser` 1.X and OpenApi 2.0, please refer to [v1 branch](https://github.com/swagger-api/swagger-parser/tree/v1)
 
 [![Build Status](https://img.shields.io/jenkins/s/https/jenkins.swagger.io/view/OSS%20-%20Java/job/oss-swagger-parser-v2.svg)](https://jenkins.swagger.io/view/OSS%20-%20Java/job/oss-swagger-parser-v2)