fix(package): update is-plain-object to version 3.0.0

Author: greenkeeper[bot]

package.json

@@ -38,7 +38,7 @@
   "dependencies": {
     "@octokit/endpoint": "^4.0.0",
     "deprecation": "^1.0.1",
-    "is-plain-object": "^2.0.4",
+    "is-plain-object": "^3.0.0",
     "node-fetch": "^2.3.0",
     "once": "^1.4.0",
     "universal-user-agent": "^2.0.1"