[WIP] kitura: update to Swift 5.2

[djones6]

Checklist:

• [x] Read the Code of Conduct and Contributing Guidelines.

• [x] Followed the commit message guidelines.

• [x] Stack adheres to Appsody stack structure.

Modifying an existing stack:

• [x] Updated the stack version in stack.yaml

Updates the Kitura stack to Swift 5.2 (depends on #779 - needs rebasing once that is merged)

Related Issues:

[Kamran64]

@djones6 @ianpartridge any update on this PR now that #779 has been merged?