upgrade dependencies

[ehennum]

Including compile okhttp -- at 4.7.2 using kotlin 1.3.71 -- and jackson -- at 2.11.1 -- as of this writing

With sufficient lead time prior to release for stability.

[ehennum]

Updated library dependencies; upgrading Gradle will require refactoring of some build.gradle tasks.

[aclavio]

When attempting to build a project without the jcenter repository I noticed that this project cannot resolve the okhttp-digest dependency. Looks like it has moved from jcenter to maven central under a new groupId:

This artifact has moved from jcenter to maven central! The coordinates have changed from
com.burgstaller:okhttp-digest: to io.github.rburgst:okhttp-digest:
https://github.com/rburgst/okhttp-digest

I suggest removing the jcenter repository as part of this ticket and updating dependencies accordingly.

[ehennum]

Thanks for calling attention to it, @aclavio; JCenter is shutting down on May 1st:

https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/