Update Dependabot configuration for JS dependencies (#477)

Removed limit on opening PRs for JS dependencies and added npm update
group.

Author: JohnGarbutt

.github/dependabot.yml

@@ -40,9 +40,9 @@ updates:
     schedule:
       # Check for new versions daily
       interval: daily
-    # Don't open PRs for JS dependencies for now, as we don't have any
-    # way of testing them
-    open-pull-requests-limit: 0
+    groups:
+      npm-updates:
+        patterns: ["*"]
     labels:
       - automation
       - javascript