Handle dependencies via Dependabot

The mkdocs-deploy-gh-pages version has been freezed, and it will be
semi-automatically updated via Dependabot.

The pip requirements file will also be handled via Dependabot.
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 0000000..4941da4
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,11 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+
+  - package-ecosystem: "pip"
+    directory: "/"
+    schedule:
+      interval: "daily"
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index b276734..dd5c44f 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -13,6 +13,6 @@
         uses: actions/checkout@v1
 
       - name: Deploy docs
-        uses: mhausenblas/mkdocs-deploy-gh-pages@master
+        uses: mhausenblas/mkdocs-deploy-gh-pages@v1.16
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}