Merge rust-bitcoin/rust-bitcoincore-rpc#339: Upgrade `jsonrpc` to ver… #106

Job	Run time
Test - nightly toolchain (minimal)	40s
Test - stable toolchain (minimal)	39s
Test - 1.56.1 toolchain (minimal)	2m 54s
Test - nightly toolchain (recent)	45s
Test - stable toolchain (recent)	44s
Test - 1.56.1 toolchain (recent)	2m 54s
Integration tests - stable toolchain (0.18.0)	47s
Integration tests - stable toolchain (0.18.1)	49s
Integration tests - stable toolchain (0.19.0.1)	1m 10s
Integration tests - stable toolchain (0.19.1)	58s
Integration tests - stable toolchain (0.20.0)	1m 13s
Integration tests - stable toolchain (0.20.1)	58s
Integration tests - stable toolchain (0.21.0)	1m 7s
	15m 38s

Provide feedback