use whitelist instead of ignore

.npmignore

@@ -1,2 +0,0 @@
-logo
-tests

package.json

@@ -1,8 +1,11 @@
 {
   "name": "greenlock",
-  "version": "2.3.1",
+  "version": "2.3.2",
   "description": "Let's Encrypt for node.js on npm",
   "main": "index.js",
+  "files": [
+    "lib"
+  ],
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"
   },