Merge pull request MongoEngine#2487 from bagerard/prepare_0_23_0

update changelog for 0.23.0 release

Merge pull request MongoEngine#2453 from bagerard/prepare_0_22_1

Update changelog for 0.22.1

Merge pull request MongoEngine#2447 from bagerard/_changelog_0_22_0

prepare 0.22.0

Merge pull request MongoEngine#2424 from bagerard/bump_0_21_0

Prepare 0.21.0 release

Merge pull request MongoEngine#2319 from bagerard/prepare_0_20_0

Bump version to 0.20.0 and update CHANGELOG accordingly

Merge pull request MongoEngine#2233 from bagerard/release_0_19_1

Bump version to 0.19.1 + force pillow to be < 7.0.0

fix pypi deployment version match

Bump version to v0.18.2

Merge pull request MongoEngine#2091 from bagerard/release_0_18_1

Bump version number and update changelog for 0.18.1

Try a different deployment condition

This time my attempt is based on the output found in another job that didn't
trigger a deployment: https://travis-ci.org/MongoEngine/mongoengine/jobs/544664203

```
/home/travis/.travis/job_stages: line 660: expected `)'
/home/travis/.travis/job_stages: line 660: syntax error near `AND'
/home/travis/.travis/job_stages: line 660: `  if [[ ($TRAVIS_REPO_SLUG = "MongoEngine/mongoengine") && ($TRAVIS_PYTHON_VERSION = 2.7) && ($PYMONGO = 3.x AND $MONGODB = 3.4) && ("$TRAVIS_TAG" != "") ]]; then'
```

See 80ca636 and
40ba51a for my previous attempts.