ci: only publish required files

See https://docs.npmjs.com/cli/v6/configuring-npm/package-json#files for details

package.json

@@ -3,6 +3,11 @@
   "version": "2.0.0",
   "description": "Tiny language and engine for selecting specific parts of a JS object, hiding the rest.",
   "main": "lib/index",
+  "files":[
+    "bin",
+    "build",
+    "lib"
+  ],
   "scripts": {
     "test": "npm run lint && mocha",
     "test:all": "nve --parallel 14,16,18 mocha",