Bumped checkout to v3 for GitHub Action

Bumped nokogiri from 1.12.5 to 1.13.3 in /docs

.github/workflows/build.yml

@@ -17,7 +17,7 @@ jobs:
   steps:
 
   - name: Clone sfall
-    uses: actions/checkout@v2
+    uses: actions/checkout@v3
 
   # Action is used twice for self-testing only
   # DevXP build results are intentionally *not* included in artifact

.github/workflows/gh-pages.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Setup Python
         uses: actions/setup-python@v2