Update dependabot.yml

Keeps producing ruby security warnings that seem to be outdated versions https://github.com/InnerSourceCommons/InnerSourcePatterns/security/dependabot/40 for the book scripts.

Author: lenucksi

.github/dependabot.yml

@@ -4,3 +4,7 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
+  - package-ecosystem: "bundler"
+    directory: "/"
+    schedule:
+      interval: "weekly"