Fix missing GitHub Sponsor to funding field in package.json (#67)

Ref https://github.com/sponsors/stylelint

To verify this change, run `npm fund` like this:

```sh-session
$ npm fund .
1: opencollective funding available at the following URL: https://opencollective.com/stylelint
2: github funding available at the following URL: https://github.com/sponsors/stylelint
Run `npm fund [<package-spec>] --which=1`, for example, to open the first funding URL listed in that package
```

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Changed: bump `npm-package-json-lint` to `^8.0.0`.
 - Changed: bump `npm-package-json-lint-config-default` to `^7.0.0`.
+- Fixed: missing GitHub Sponsor to `funding` field in `package.json`.
 
 ## 5.0.1
 

package.json

@@ -8,10 +8,16 @@
     "npm-package-json-lint-config"
   ],
   "repository": "stylelint/npm-package-json-lint-config",
-  "funding": {
-    "type": "opencollective",
-    "url": "https://opencollective.com/stylelint"
-  },
+  "funding": [
+    {
+      "type": "opencollective",
+      "url": "https://opencollective.com/stylelint"
+    },
+    {
+      "type": "github",
+      "url": "https://github.com/sponsors/stylelint"
+    }
+  ],
   "license": "MIT",
   "author": "stylelint",
   "main": "lib/npm-package-json-lint-config.js",