add support for pull_request_target event (#2)

Co-authored-by: Stephen Belanger <admin@stephenbelanger.com>

src/action.js

@@ -7,9 +7,14 @@ const {
   toMarkdown
 }= require('./')
 
+const events = new Set([
+  'pull_request',
+  'pull_request_target'
+])
+
 async function createOrUpdateIssueComment (message) {
   info(`Event type ${context.eventName}`)
-  if (context.eventName !== 'pull_request') return
+  if (!events.has(context.eventName)) return
 
   const sig = '<sub>🤖 This report was automatically generated by [heaviest-objects-in-the-universe](https://github.com/qard/heaviest-objects-in-the-universe/)<sub>'
   const body = [message, sig].join('\n\n')