Tag release v4.2.0

[KipSigei]

Changes

Bump version to v4.2.0

Release notes

New Features

• https://github.com/onaio/onadata/pull/2504

Bug Fixes

• https://github.com/onaio/onadata/pull/2598
• https://github.com/onaio/onadata/pull/2600

Enhancements

• https://github.com/onaio/onadata/pull/2595
• https://github.com/onaio/onadata/pull/2597
• https://github.com/onaio/onadata/pull/2599