[dashpay/dash] Adjust diff for slow testnet/devnet blocks a bit smoother (#2161)

Bumped `chainwork` condition to `000000000000000000000000000000000000000000000000003ff00000000000` (current work is `000000000000000000000000000000000000000000000000003f4df1127fecc9` already). Also, 2x (5 minutes blocks) seems to occur way too often, so bumped it to 4x (10 minutes). Pls re-review.

This post was last modified on July 7, 2018, 1:56 pm