Bump google-cloud-datastore from 1.10.0 to 2.1.6

Bumps [google-cloud-datastore](https://github.com/googleapis/python-datastore) from 1.10.0 to 2.1.6.
- [Release notes](https://github.com/googleapis/python-datastore/releases)
- [Changelog](https://github.com/googleapis/python-datastore/blob/master/CHANGELOG.md)
- [Commits](https://github.com/googleapis/python-datastore/compare/v1.10.0...v2.1.6)

---
updated-dependencies:
- dependency-name: google-cloud-datastore
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -2,7 +2,7 @@ beautifulsoup4==4.8.1
 dnspython==1.16.0
 feedparser==5.2.1
 GitPython
-google-cloud-datastore==1.10.0
+google-cloud-datastore==2.1.6
 html-similarity==0.3.2
 httpretty==0.9.7
 pyopenssl==18.0.0