[dependabot] Manage Docker versions (#59)

Author: IsaacG

.github/dependabot.yml

@@ -2,7 +2,13 @@ version: 2
 
 updates:
   # Keep dependencies for GitHub Actions up-to-date
-  - package-ecosystem: "github-actions"
-    directory: "/"
+  - package-ecosystem: github-actions
+    directory: /
     schedule:
-      interval: 'monthly'
+      interval: monthly
+
+  # Enable updates to the dependencies of our Dockerfile
+  - package-ecosystem: docker
+    directory: /
+    schedule:
+      interval: monthly