Change default branch name to main (yahoo#99)

Author: okuryu

.github/workflows/test.yml

@@ -2,9 +2,9 @@ name: Test
 
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
-    branches: [master]
+    branches: [main]
 
 jobs:
   build:

README.md

@@ -141,4 +141,4 @@ See the [LICENSE file][LICENSE] for license text and copyright information.
 [travis-badge]: https://img.shields.io/travis/yahoo/serialize-javascript.svg?style=flat-square
 [express-state]: https://github.com/yahoo/express-state
 [JSON.stringify]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
-[LICENSE]: https://github.com/yahoo/serialize-javascript/blob/master/LICENSE
+[LICENSE]: https://github.com/yahoo/serialize-javascript/blob/main/LICENSE