chore: release 2.9.0 (#205)

🤖 I have created a release \*beep\* \*boop\*
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## [2.9.0](https://www.github.com/googleapis/nodejs-document-ai/compare/v2.8.0...v2.9.0) (2021-04-26)


### Features

* add confidence field to the PageAnchor.PageRef in document.proto ([#204](https://www.github.com/googleapis/nodejs-document-ai/issues/204)) ([580150b](https://www.github.com/googleapis/nodejs-document-ai/commit/580150bdb3b5f7bfac599ee7c122a3ffb9a624c7))
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This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).

Author: release-please[bot]

document-ai/package.json

@@ -13,7 +13,7 @@
     "test": "mocha test/*.js --timeout 600000"
   },
   "dependencies": {
-    "@google-cloud/documentai": "^2.8.0",
+    "@google-cloud/documentai": "^2.9.0",
     "@google-cloud/storage": "^5.0.0",
     "p-queue": "^6.6.2",
     "uuid": "^8.3.1"