Use import {Octokit} (#332)

* Use import {Octokit}

* Update @octokit/rest to 16.43.1

package.json

@@ -39,7 +39,7 @@
   "dependencies": {
     "@actions/http-client": "^1.0.3",
     "@octokit/graphql": "^4.3.1",
-    "@octokit/rest": "^16.15.0"
+    "@octokit/rest": "^16.43.1"
   },
   "devDependencies": {
     "jest": "^24.7.1",