Switch workflow back to macOS.

.github/workflows/build.yml

@@ -4,7 +4,7 @@ name: Build
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: macOS-latest
 
     strategy:
       matrix:
@@ -12,6 +12,11 @@ jobs:
 
     steps:
 
+    - name: Checkout
+      uses: actions/checkout@v2
+      with:
+        submodules: true
+
     - name: Get Gem Installation Directory
       id: get-gemdir
       run: |
@@ -48,11 +53,6 @@ jobs:
     - name: Setup HTMLProofer
       run: sudo gem install html-proofer
 
-    - name: Checkout
-      uses: actions/checkout@v2
-      with:
-        submodules: true
-
     - name: Build website
       run: make build