chore(deps): update npm to v6.9.0 (#476)

Author: renovate[bot]

package-lock.json

@@ -72,7 +72,7 @@
   },
   "engines": {
     "node": "10.15.3",
-    "npm": "6.8.0"
+    "npm": "6.9.0"
   },
   "dependencies": {
     "@woocommerce/components": "1.6.0",