use not_planned close reason

lib/stale.js

@@ -155,7 +155,7 @@ module.exports = class Stale {
       if (closeComment) {
         await this.github.issues.createComment({ owner, repo, number, body: closeComment })
       }
-      return this.github.issues.edit({ owner, repo, number, state: 'closed' })
+      return this.github.issues.update({ owner, repo, number, state: 'closed', state_reason: 'not_planned' })
     } else {
       this.logger.info('%s/%s#%d would have been closed (dry-run)', owner, repo, number)
     }

test/stale.test.js

@@ -30,7 +30,7 @@ describe('stale', () => {
         createLabel: issueAction,
         addLabels: issueAction,
         createComment: issueAction,
-        edit: issueAction
+        update: issueAction
       },
       search: {
         issues: issueAction
@@ -108,8 +108,9 @@ describe('stale', () => {
         comments++
         return Promise.resolve(notFoundError)
       })
-      github.issues.edit = ({ owner, repo, number, state }) => {
+      github.issues.update = ({ owner, repo, number, state, state_reason }) => {
         if (state === 'closed') {
+          expect(state_reason).toBe('not_planned')
           closed++
         }
       }