chore: release 2.12.0 (#143)

🤖 I have created a release \*beep\* \*boop\*
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## [2.12.0](https://www.github.com/googleapis/nodejs-dialogflow-cx/compare/v2.11.0...v2.12.0) (2021-06-30)


### Features

* mark agent.default_language_code as required feat: add return_partial response to Fulfillment docs: add notes to train agent before sending queries ([#140](https://www.github.com/googleapis/nodejs-dialogflow-cx/issues/140)) ([eae8f44](https://www.github.com/googleapis/nodejs-dialogflow-cx/commit/eae8f4409cf5832c5fd28e2e676847a4722997b9))


### Bug Fixes

* **deps:** google-gax v2.17.0 with mTLS ([#145](https://www.github.com/googleapis/nodejs-dialogflow-cx/issues/145)) ([d5f2918](https://www.github.com/googleapis/nodejs-dialogflow-cx/commit/d5f291886d1418ad43684d3db7b0a2d12cd8c219))
* make request optional in all cases ([#139](https://www.github.com/googleapis/nodejs-dialogflow-cx/issues/139)) ([ad950f0](https://www.github.com/googleapis/nodejs-dialogflow-cx/commit/ad950f057f413b9c094b6d23a21ada0d64887206))
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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]

dialogflow-cx/package.json

@@ -13,7 +13,7 @@
     "test": "c8 mocha --timeout 600000 test/*.js"
   },
   "dependencies": {
-    "@google-cloud/dialogflow-cx": "^2.11.0",
+    "@google-cloud/dialogflow-cx": "^2.12.0",
     "uuid": "^8.3.1"
   },
   "devDependencies": {