Sort calculated checksum

[blabno]

When I add new dependency to my project and run calculateChecksums
Then git diff should show me minimal differences.

This can be achieved if dependencies are sorted by groupId and artifactName;

https://github.com/signalapp/gradle-witness/blob/master/src/main/groovy/org/whispersystems/witness/WitnessPlugin.groovy#L56