README.md - CI branch reference

Author: martinsumner

README.md

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 ## Introduction
 
-[![Build Status](https://github.com/martinsumner/leveled/actions/workflows/erlang.yml/badge.svg?branch=develop-3.1)](https://github.com/martinsumner/leveled/actions)
+[![Build Status](https://github.com/martinsumner/leveled/actions/workflows/erlang.yml/badge.svg?branch=develop-3.4)](https://github.com/martinsumner/leveled/actions)
 
 Leveled is a simple Key-Value store based on the concept of Log-Structured Merge Trees, with the following characteristics: