add pkijs for reading expiresAt

package.json

@@ -29,14 +29,16 @@
     "url": "https://github.com/Daplie/node-letsencrypt/issues"
   },
   "homepage": "https://github.com/Daplie/node-letsencrypt#readme",
-  "devDependencies": {
-  },
+  "devDependencies": {},
   "optionalDependencies": {},
   "dependencies": {
+    "asn1": "^0.2.3",
     "bluebird": "^3.0.6",
     "homedir": "^0.6.0",
     "letiny-core": "^2.0.1",
     "mkdirp": "^0.5.1",
+    "node.extend": "^1.1.5",
+    "pkijs": "^1.3.27",
     "pyconf": "^1.1.2",
     "request": "^2.67.0",
     "rsa-compat": "^1.2.1",