use json encoding for post data to blockchainAPI
use json encoding for post data to blockchainAPI

It seems Insight used to support urlencoded data, but now only supports JSON
data. I think this explains all the weirdness I have had interacting with the
two different versions of Insight. The mainnet version hosted at
insight.bitpay.com accepts urlencoded data, and the testnet version of
test-insight.bitpay.com does not. I just have to be sure to pass in JSON
encoded data, and things seem to work. I can probably go back and change how
I'm retrieving UTXOs to use a POST request now, since that was probably why it
wasn't working before.

ryanxcharles/datt,yoursnetwork/yours-core,ryanxcharles/datt,dattnetwork/datt,yoursnetwork/yours-core,dattnetwork/datt