chore: add @wordpress/npm-package-json-lint-config

Author: ntwb

packages/stylelint-config-wordpress/package.json

@@ -38,6 +38,7 @@
 	"devDependencies": {
 		"@commitlint/cli": "^7.0.0",
 		"@commitlint/config-conventional": "^7.0.1",
+		"@wordpress/npm-package-json-lint-config": "^1.1.2",
 		"eslint": "^5.4.0",
 		"eslint-plugin-jest": "^21.21.0",
 		"eslint-plugin-wordpress": "git://github.com/WordPress-Coding-Standards/eslint-plugin-wordpress.git#b65ae0cea1199c9714641ed3be7ea98fcb27dd6c",
@@ -84,6 +85,17 @@
 		],
 		"verbose": true
 	},
+	"npmPackageJsonLintConfig": {
+		"extends": "@wordpress/npm-package-json-lint-config",
+		"rules": {
+			"valid-values-license": [
+				"error",
+				[
+					"MIT"
+				]
+			]
+		}
+	},
 	"remarkConfig": {
 		"presets": [
 			"lint-recommended",