Upgrade build and test environment to allow use of Django >= 2.2 #135
Description
The TravisCI build environment uses an older package of sqlite.
In turn, this requires a Django version less than 2.2 to be used for the tests, and this is impinging on the packaging requirements as they are also used to fix the test environment.
Therefore the CI build should be configured to use a newer build image, which will in turn provide a later version of sqlite and thus enable the package restriction to be removed.