chore: update npm dependencies with dependabot (#52)

In particular, this will update @maxgraph/core automatically when a new
release is available.

.github/dependabot.yml

@@ -2,6 +2,20 @@
 
 version: 2
 updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 2
+    versioning-strategy: increase
+    rebase-strategy: "disabled"
+    commit-message:
+      prefix: "chore(deps)"
+      prefix-development: "chore(deps-dev)"
+    groups:
+      development-dependencies:
+        dependency-type: "development"
+
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: