Allow Dependabot to update package.json

As per the industry standard, all version numbers are specified in package.json, so Dependabot is allowed to suggest increases when a new version is released. This is the default.

Discussed in https://community.openfoodnetwork.org/t/javascript-dependency-management-with-package-json/2753

.github/dependabot.yml

@@ -6,10 +6,12 @@ updates:
     schedule:
       interval: "daily"
     open-pull-requests-limit: 10
+    # Only specific requirements are specified in Gemfile, so don't touch it.
     versioning-strategy: lockfile-only
 
   - package-ecosystem: "npm"
     directory: "/"
     schedule:
       interval: "daily"
-    versioning-strategy: lockfile-only
+    # All versions are specified in package.json, so please update them.
+    versioning-strategy: increase