ci: add macOS 11 Big Sur

Remove all traces of Travis CI

Change-Id: Ie9ad527af4921c4f3c56903851200131ed0d5e87
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 20f7cb4..e988485 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,7 +5,6 @@
       - 'docs/**'
       - '*.md'
       - '.mailmap'
-      - '.travis.yml'
   workflow_dispatch:
 
 permissions:
@@ -49,9 +48,14 @@
       matrix:
         xcode: ['11.3', '11.7', '12.4']
         os: [macos-10.15]
+        include:
+          - xcode: '12.5'
+            os: macos-11
+          - xcode: '13'
+            os: macos-11
     runs-on: ${{ matrix.os }}
     env:
-      NODE_LABELS: OSX OSX-10.15
+      NODE_LABELS: OSX
       WAF_JOBS: 3
     steps:
       - name: Set up Xcode