Change default branch name from master to main

Author: mxie

README.md

@@ -4,8 +4,7 @@ A GitHub Action that closes issues whose titles include a date that's in the
 past.
 
 Dates are assumed to be in the format of `MM-DD-YY[YY]` where `-` could be any
-delimeter. The year part is also ignored because why would you date something
-before the year 2000?
+delimeter.
 
 ## Usage
 
@@ -19,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Close issues
-      uses: mxie/close-outdated-issues-action@master
+      uses: mxie/close-outdated-issues-action@main
       with:
         token: ${{ secrets.GITHUB_TOKEN }}
 ```