docs(readme): update build status branch

README.md

@@ -55,4 +55,4 @@ Interactively update packages to the latest versions from the npm registry, wher
 - [![support on ko-fi](https://ko-fi.com/img/githubbutton_sm.svg)](https://ko-fi.com/C0C4PY4P)
 - [![NPM version](http://img.shields.io/npm/v/syncpack.svg?style=flat-square)](https://www.npmjs.com/package/syncpack)
 - [![NPM downloads](http://img.shields.io/npm/dm/syncpack.svg?style=flat-square)](https://www.npmjs.com/package/syncpack)
-- [![Build Status](https://img.shields.io/github/actions/workflow/status/JamieMason/syncpack/ci.yaml?branch=master)](https://github.com/JamieMason/syncpack/actions)
+- [![Build Status](https://img.shields.io/github/actions/workflow/status/JamieMason/syncpack/ci.yaml?branch=main)](https://github.com/JamieMason/syncpack/actions)