use updated rust-bitcoincore-rpc and consequently bitcoin 0.28.0

Author: RCasatta

Cargo.toml

@@ -9,7 +9,7 @@ documentation = "https://docs.rs/bitcoind/"
 edition = "2018"
 
 [dependencies]
-bitcoincore-rpc = "0.14.0"
+bitcoincore-rpc = "0.15.0"
 tempfile = "3.1"
 log = "0.4"
 home = "0.5.3"  # use same ver in build-dep