update default branch name

Author: visr

.github/workflows/CI.yml

@@ -3,7 +3,7 @@ on:
   pull_request:
   push:
     branches:
-      - master
+      - main
     tags: '*'
 jobs:
   test:

README.md

@@ -3,7 +3,7 @@
 [![](https://img.shields.io/badge/docs-stable-blue.svg)](https://JuliaGeo.github.io/GeoJSON.jl/stable)
 [![](https://img.shields.io/badge/docs-dev-blue.svg)](https://JuliaGeo.github.io/GeoJSON.jl/dev)
 [![CI](https://github.com/JuliaGeo/GeoJSON.jl/workflows/CI/badge.svg)](https://github.com/JuliaGeo/GeoJSON.jl/actions?query=workflow%3ACI)
-[![codecov](https://codecov.io/gh/JuliaGeo/GeoJSON.jl/branch/master/graph/badge.svg?token=ccpOaPSi08)](https://codecov.io/gh/JuliaGeo/GeoJSON.jl)
+[![codecov](https://codecov.io/gh/JuliaGeo/GeoJSON.jl/branch/main/graph/badge.svg?token=ccpOaPSi08)](https://codecov.io/gh/JuliaGeo/GeoJSON.jl)
 
 Read [GeoJSON](https://geojson.org/) files using [JSON3.jl](https://github.com/quinnj/JSON3.jl), and provide the [Tables.jl](https://github.com/JuliaData/Tables.jl) interface.