chore: release 2.0.0 (#572)

* updated CHANGELOG.md [ci skip]

* updated package.json [ci skip]

* updated samples/package.json

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>

Author: release-please[bot]

vision/samples/package.json

@@ -13,7 +13,7 @@
     "test": "mocha system-test --timeout 600000"
   },
   "dependencies": {
-    "@google-cloud/vision": "^1.11.0",
+    "@google-cloud/vision": "^2.0.0",
     "mathjs": "^7.0.0",
     "natural": "^2.0.0",
     "pureimage": "^0.2.1",