build: whitelist the root gatsby-node.js for npm release

Author: alvis

.presetterrc.json

@@ -1,3 +1,6 @@
 {
-  "preset": "presetter-preset"
+  "preset": "presetter-preset",
+  "config": {
+    "npmignore": ["!gatsby-node.js"]
+  }
 }