chore: rename master -> main

No change to logic. This updates the main branch name in the README.

Author: nfischer

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 ## Releasing
 
-On the latest clean `master`:
+On the latest clean `main`:
 
 ```
 npm run release:major

README.md

@@ -1,7 +1,7 @@
 # Shx
 
-[![Build Status](https://img.shields.io/endpoint.svg?url=https%3A%2F%2Factions-badge.atrox.dev%2Fshelljs%2Fshx%2Fbadge%3Fref%3Dmaster&style=flat-square)](https://actions-badge.atrox.dev/shelljs/shx/goto?ref=master)
-[![Codecov](https://img.shields.io/codecov/c/github/shelljs/shx/master.svg?style=flat-square&label=coverage)](https://codecov.io/gh/shelljs/shx)
+[![Build Status](https://img.shields.io/endpoint.svg?url=https%3A%2F%2Factions-badge.atrox.dev%2Fshelljs%2Fshx%2Fbadge%3Fref%3Dmain&style=flat-square)](https://actions-badge.atrox.dev/shelljs/shx/goto?ref=main)
+[![Codecov](https://img.shields.io/codecov/c/github/shelljs/shx/main.svg?style=flat-square&label=coverage)](https://codecov.io/gh/shelljs/shx)
 [![npm version](https://img.shields.io/npm/v/shx.svg?style=flat-square)](https://www.npmjs.com/package/shx)
 [![npm downloads](https://img.shields.io/npm/dm/shx.svg?style=flat-square)](https://www.npmjs.com/package/shx)